ASE Technology Holding (ASX) 20-F 26 Apr 19 2018 FY Annual report (foreign) Financial data

Document and Entity Information

Document and Entity Information - shares	12 Months Ended
	Dec. 31, 2018	Jan. 31, 2019
Document and entity information [abstract]
Document Type	20-F
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Trading Symbol	ASX
Entity Registrant Name	ASE TECHNOLOGY HOLDING CO., LTD.
Entity Central Index Key	0001122411
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		4,322,321,982

Consolidated Balance Sheets

Consolidated Balance Sheets $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
CURRENT ASSETS
Cash and cash equivalents	$ 1,683,059	$ 51,518,436	$ 46,078,066
Financial assets at fair value through profit or loss - current	237,250	7,262,227	5,223,067
Available-for-sale financial assets - current			89,159
Contract assets - current	146,635	4,488,500
Trade receivables, net	2,596,581	79,481,359	55,200,706
Other receivables	41,920	1,283,180	1,051,955
Current tax assets	17,127	524,263	260,542
Inventories	1,196,584	36,627,451	24,260,911
Inventories related to real estate business	328,671	10,060,608	9,819,516
Other financial assets - current	213,638	6,539,467	472,340
Other current assets	123,273	3,773,384	2,482,010
Total current assets	6,584,738	201,558,875	144,938,272
NON-CURRENT ASSETS
Financial assets at fair value through profit or loss - non-current	20,785	636,231
Financial assets at fair value through other comprehensive income - non-current	52,183	1,597,323
Available-for-sale financial assets - non-current			1,123,006
Investments accounted for using the equity method	304,224	9,312,308	48,753,751
Property, plant and equipment	7,010,539	214,592,588	135,168,406
Investment properties	252,806	7,738,379	8,119,436
Goodwill	1,632,618	49,974,446	9,934,494
Other intangible assets	1,009,399	30,897,700	1,406,865
Deferred tax assets	166,885	5,108,357	4,001,821
Other financial assets - non-current	34,116	1,044,294	1,170,500
Long-term prepayments for lease	351,677	10,764,835	8,851,330
Other non-current assets	27,331	836,591	454,391
Total non-current assets	10,862,563	332,503,052	218,984,000
Total assets	17,447,301	534,061,927	363,922,272
CURRENT LIABILITIES
Short-term borrowings	1,413,377	43,263,469	17,962,471
Financial liabilities at fair value through profit or loss - current	1,197	36,655	677,430
Financial liabilities for hedging - current	127,397	3,899,634
Trade payables	1,858,351	56,884,116	41,672,233
Other payables	1,012,868	31,003,882	21,377,887
Current tax liabilities	221,533	6,781,136	7,619,328
Current portion of bonds payable			6,161,197
Current portion of long-term borrowings	352,141	10,779,034	8,261,625
Other current liabilities	195,497	5,984,156	4,644,566
Total current liabilities	5,182,361	158,632,082	108,376,737
NON-CURRENT LIABILITIES
Bonds payable	554,915	16,985,936	16,981,583
Long-term borrowings	4,152,868	127,119,295	27,145,003
Deferred tax liabilities	189,700	5,806,713	4,961,487
Net defined benefit liabilities	167,222	5,118,677	3,936,685
Other non-current liabilities	44,799	1,371,302	1,210,590
Total non-current liabilities	5,109,504	156,401,923	54,235,348
Total liabilities	10,291,865	315,034,005	162,612,085
Share capital
Ordinary shares	1,411,352	43,201,486	87,246,194
Shares subscribed in advance	512	15,658	134,593
Total share capital	1,411,864	43,217,144	87,380,787
Capital surplus	4,680,714	143,276,664	40,624,328
Retained earnings
Legal reserve			16,765,066
Special reserve	109,570	3,353,938	3,353,938
Unappropriated earnings	666,562	20,403,477	53,599,541
Total retained earnings	776,132	23,757,415	73,718,545
Other equity	(225,537)	(6,903,681)	(6,311,089)
Treasury shares	(64,002)	(1,959,107)	(7,292,513)
Equity attributable to owners of the Company	6,579,171	201,388,435	188,120,058
NON-CONTROLLING INTERESTS	576,265	17,639,487	13,190,129
Total equity	7,155,436	219,027,922	201,310,187
TOTAL	$ 17,447,301	$ 534,061,927	$ 363,922,272

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)$ / shares	Dec. 31, 2018TWD ($)$ / shares	Dec. 31, 2017TWD ($)$ / shares	Dec. 31, 2016TWD ($)$ / shares
Statement [LineItems]
OPERATING REVENUES	$ 12,123,242	$ 371,092,421	$ 290,441,208	$ 274,884,107
OPERATING COSTS	10,125,102	309,929,371	237,708,937	221,696,922
GROSS PROFIT	1,998,140	61,163,050	52,732,271	53,187,185
OPERATING EXPENSES
Selling and marketing expenses	161,176	4,933,602	3,308,992	3,473,586
General and administrative expenses	477,586	14,618,900	12,458,054	11,662,082
Research and development expenses	488,821	14,962,799	11,746,613	11,391,147
Total operating expenses	1,127,583	34,515,301	27,513,659	26,526,815
OTHER OPERATING INCOME AND EXPENSES, NET	12,139	371,583	108,556	(800,280)
PROFIT FROM OPERATIONS	882,696	27,019,332	25,327,168	25,860,090
NON-OPERATING INCOME AND EXPENSES
Other income	35,693	1,092,558	707,754	589,236
Other gains, net	257,245	7,874,273	6,259,453	2,276,544
Finance costs	(116,571)	(3,568,241)	(1,799,494)	(2,261,075)
Share of the profit of associates and joint ventures	(15,689)	(480,244)	525,782	1,503,910
Total non-operating income and expenses	160,678	4,918,346	5,693,495	2,108,615
PROFIT BEFORE INCOME TAX	1,043,374	31,937,678	31,020,663	27,968,705
INCOME TAX EXPENSE	147,448	4,513,369	6,523,603	5,390,844
PROFIT FOR THE YEAR	895,926	27,424,309	24,497,060	22,577,861
Items that will not be reclassified subsequently to profit or loss:
Remeasurement of defined benefit obligation	(10,068)	(308,180)	205,344	(417,181)
Unrealized loss on equity investments at fair value through other comprehensive income	(13,801)	(422,441)
Share of other comprehensive income (loss) of associates and joint ventures	(18,237)	(558,217)	7,249	(49,794)
Income tax relating to items that will not be reclassified subsequently	4,406	134,853	(51,217)	73,637
Items that will not be reclassified subsequently to profit or loss	(37,700)	(1,153,985)	161,376	(393,338)
Items that may be reclassified subsequently to profit or loss:
Exchange differences on translating foreign operations	7,443	227,821	(5,287,734)	(6,445,643)
Unrealized gain (loss) on available-for-sale financial assets			224,036	(248,599)
Unrealized loss on investments in debt instruments at fair value through other comprehensive income	(2,061)	(63,076)
Share of other comprehensive income (loss) of associates and joint ventures	4,463	136,608	264,389	(871,679)
Items that may be reclassified subsequently to profit or loss	9,845	301,353	(4,799,309)	(7,565,921)
Other comprehensive loss for the year, net of income tax	(27,855)	(852,632)	(4,637,933)	(7,959,259)
TOTAL COMPREHENSIVE INCOME FOR THE YEAR	868,071	26,571,677	19,859,127	14,618,602
PROFIT FOR THE YEAR ATTRIBUTABLE TO:
Owners of the Company	856,606	26,220,721	22,819,119	21,324,423
Non-controlling interests	39,320	1,203,588	1,677,941	1,253,438
PROFIT FOR THE YEAR	895,926	27,424,309	24,497,060	22,577,861
TOTAL COMPREHENSIVE INCOME FOR THE YEAR ATTRIBUTABLE TO:
Owners of the Company	836,996	25,620,461	18,524,067	13,956,976
Non-controlling interests	31,075	951,216	1,335,060	661,626
TOTAL COMPREHENSIVE INCOME FOR THE YEAR	$ 868,071	$ 26,571,677	$ 19,859,127	$ 14,618,602
EARNINGS PER SHARE
Basic | (per share)	$ 0.20	$ 6.18	$ 5.59	$ 5.57
Diluted | (per share)	0.20	6.07	5.19	4.66
American depositary shares [member]
EARNINGS PER SHARE
Basic | (per share)	0.40	12.35	11.18	11.13
Diluted | (per share)	$ 0.40	$ 12.14	$ 10.38	$ 9.31

Consolidated Statements of Chan

Consolidated Statements of Changes in Equity $ in Thousands, $ in Thousands	USD ($)	TWD ($)	Share capital [member]USD ($)shares	Share capital [member]TWD ($)shares	Capital surplus [member]USD ($)	Capital surplus [member]TWD ($)	Legal reserve [member]TWD ($)	Special reserve [member]USD ($)	Special reserve [member]TWD ($)	Unappropriated earnings [member]USD ($)	Unappropriated earnings [member]TWD ($)	Retained earnings [member]USD ($)	Retained earnings [member]TWD ($)	Exchange differences on translating foreign operations [member]USD ($)	Exchange differences on translating foreign operations [member]TWD ($)	Unrealized gain (loss) on available-for-sale financial assets [member]TWD ($)	Unrealized gain (loss) on financial assets at fair value through other comprehensive income [member]USD ($)	Unrealized gain (loss) on financial assets at fair value through other comprehensive income [member]TWD ($)	Other equity[member]USD ($)	Other equity[member]TWD ($)	Treasury shares [member]USD ($)	Treasury shares [member]TWD ($)	Equity Attributable to Owners of the Company [member]USD ($)	Equity Attributable to Owners of the Company [member]TWD ($)	Non-controlling interests [member]USD ($)	Non-controlling interests [member]TWD ($)
Balance at January 1 at Dec. 31, 2015		$ 165,924,980		$ 79,185,660		$ 23,758,550	$ 12,649,145		$ 3,353,938		$ 37,696,865		$ 53,699,948		$ 4,492,671	$ 588,119				$ 5,080,790		$ (7,292,513)		$ 154,432,435		$ 11,492,545
Beginning balance, shares at Dec. 31, 2015 | shares			7,910,428,000	7,910,428,000
Change from investments in associates and joint ventures accounted for using the equity method		95,495				51,959										43,536				43,536				95,495
Net profit for the year		22,577,861									21,324,423		21,324,423											21,324,423		1,253,438
Other comprehensive income (loss) for the year, net of income tax		(7,959,259)									(402,184)		(402,184)		(6,136,294)	(828,969)				(6,965,263)				(7,367,447)		(591,812)
Total comprehensive income (loss)		14,618,602									20,922,239		20,922,239		(6,136,294)	(828,969)				(6,965,263)				13,956,976		661,626
Appropriation of earnings
Legal reserve							1,947,887				(1,947,887)
Cash dividends distributed by the Company		(12,476,779)									(12,476,779)		(12,476,779)											(12,476,779)
Appropriated retained earnings		(12,476,779)					1,947,887				(14,424,666)		(12,476,779)											(12,476,779)
Issue of dividends received by subsidiaries from the Company		233,013				233,013																		233,013
Partial disposal of interests in subsidiaries and additional acquisition of majority-owned subsidiaries						(20,552)					(5,884)		(5,884)											(26,436)		26,436
Changes in percentage of ownership interest in subsidiaries		(2,825,773)				(1,912,887)																		(1,912,887)		(912,886)
Issue of ordinary shares under employee share options		983,117		$ 382,380		600,737																		983,117
Issue of ordinary shares under employee share options, shares			35,756,000	35,756,000
Non-controlling interests arising from acquisition of subsidiaries		42,857																								42,857
Cash dividends distributed by subsidiaries		(237,850)																								(237,850)
Additional non-controlling interest arising on issue of employee share options by subsidiaries		483,503				(444,320)																		(444,320)		927,823
Balance at December 31 at Dec. 31, 2016		166,841,165		$ 79,568,040		22,266,500	14,597,032		3,353,938		44,188,554		62,139,524		(1,643,623)	(197,314)				(1,840,937)		(7,292,513)		154,840,614		12,000,551
Ending balance, shares at Dec. 31, 2016 | shares			7,946,184,000	7,946,184,000
Change from investments in associates and joint ventures accounted for using the equity method		1,490				1,490																		1,490
Net profit for the year		24,497,060									22,819,119		22,819,119											22,819,119		1,677,941
Other comprehensive income (loss) for the year, net of income tax		(4,637,933)									175,100		175,100		(5,090,036)	619,884				(4,470,152)				(4,295,052)		(342,881)
Total comprehensive income (loss)		19,859,127									22,994,219		22,994,219		(5,090,036)	619,884				(4,470,152)				18,524,067		1,335,060
Appropriation of earnings
Legal reserve							2,168,034				(2,168,034)
Cash dividends distributed by the Company		(11,415,198)									(11,415,198)		(11,415,198)											(11,415,198)
Appropriated retained earnings		(11,415,198)					2,168,034				(13,583,232)		(11,415,198)											(11,415,198)
Issue of ordinary shares for capital increase by cash		10,290,000		$ 3,000,000		7,290,000																		10,290,000
Issue of ordinary shares for capital increase by cash, shares | shares			300,000,000	300,000,000
Issue of ordinary shares under conversion of bonds		13,900,482		$ 4,242,577		9,657,905																		13,900,482
Issue of ordinary shares under conversion of bonds, shares | shares			424,258,000	424,258,000
Issue of dividends received by subsidiaries from the Company		200,977				200,977																		200,977
Changes in percentage of ownership interest in subsidiaries						3,055																		3,055		(3,055)
Issue of ordinary shares under employee share options		1,667,759		$ 570,170		1,256,789																		1,826,959		(159,200)
Issue of ordinary shares under employee share options, shares			67,637,000	67,637,000
Cash dividends distributed by subsidiaries		(246,440)																								(246,440)
Additional non-controlling interest arising on issue of employee share options by subsidiaries		210,825				(52,388)																		(52,388)		263,213
Balance at December 31 (Adjusted Balance [member]) at Dec. 31, 2017		201,914,633		$ 87,380,787		40,624,328	16,765,066		3,353,938		54,485,857		74,604,861		(6,733,659)			$ 135,517		(6,598,142)		(7,292,513)		188,719,321		13,195,312
Balance at December 31 at Dec. 31, 2017		201,310,187		$ 87,380,787		40,624,328	16,765,066		3,353,938		53,599,541		73,718,545	$ (219,982)	(6,733,659)	422,570				(6,311,089)		(7,292,513)		188,120,058		13,190,129
Ending balance, shares at Dec. 31, 2017 | shares			8,738,079,000	8,738,079,000
Effect of retrospective applications		604,446									886,316		886,316			$ (422,570)		135,517		(287,053)				599,263		5,183
Change from investments in associates and joint ventures accounted for using the equity method		1,500,100				1,411,899					88,201		88,201											1,500,100
Cash dividends paid from the capital surplus		(10,795,980)				(10,795,980)																		(10,795,980)
Other changes in the capital surplus		872				872																		872
Net profit for the year	$ 895,926	27,424,309									26,220,721		26,220,721											26,220,721		1,203,588
Other comprehensive income (loss) for the year, net of income tax	(27,855)	(852,632)									(146,194)		(146,194)		562,794			(1,016,860)		(454,066)				(600,260)		(252,372)
Total comprehensive income (loss)	868,071	26,571,677									26,074,527		26,074,527		562,794			(1,016,860)		(454,066)				25,620,461		951,216
Appropriation of earnings
Effect of the joint share exchange				$ (43,183,919)		117,693,658	$ (16,765,066)				(57,744,673)		(74,509,739)
Effect of the joint share exchange, shares | shares			(4,318,392,000)	(4,318,392,000)
Buy-back of ordinary shares		(71,302)																				(71,302)		(71,302)
Cancellation of treasury shares				$ (1,218,520)		(1,480,903)					(2,705,285)		(2,705,285)									5,404,708
Cancellation of treasury shares, shares | shares			(121,852,000)	(121,852,000)
Issue of dividends received by subsidiaries from the Company		182,354				182,354																		182,354
Disposal of interest in associates and joint ventures accounted for using the equity method		(1,055,118)				(1,408,495)					204,450		204,450		282,291			(133,364)		148,927				(1,055,118)
Differences between consideration and carrying amount arising from acquisition or disposal of subsidiaries		1,640,159				(1,142,856)																		(1,142,856)		2,783,015
Changes in percentage of ownership interest in subsidiaries		(1,919,986)				(1,118,102)																		(1,118,102)		(801,884)
Issue of ordinary shares under employee share options		788,141		$ 238,796		549,345																		788,141
Issue of ordinary shares under employee share options, shares			23,879,000	23,879,000
Cash dividends distributed by subsidiaries		(424,815)																								(424,815)
Additional non-controlling interest arising on issue of employee share options by subsidiaries		697,187				(1,239,456)																		(1,239,456)		1,936,643
Fair value through other comprehensive income - equity instruments											400		400					(400)		(400)
Balance at December 31 at Dec. 31, 2018	$ 7,155,436	$ 219,027,922	$ 1,411,864	$ 43,217,144	$ 4,680,714	$ 143,276,664		$ 109,570	$ 3,353,938	$ 666,562	$ 20,403,477	$ 776,132	$ 23,757,415	$ (192,374)	$ (5,888,574)		$ (33,163)	$ (1,015,107)	$ (225,537)	$ (6,903,681)	$ (64,002)	$ (1,959,107)	$ 6,579,171	$ 201,388,435	$ 576,265	$ 17,639,487
Ending balance, shares at Dec. 31, 2018 | shares			4,321,714,000	4,321,714,000

Consolidated Statements of Cash

Consolidated Statements of Cash Flows $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
CASH FLOWS FROM OPERATING ACTIVITIES
Profit before income tax	$ 1,043,374	$ 31,937,678	$ 31,020,663	$ 27,968,705
Adjustments for:
Depreciation expense	1,316,121	40,286,453	28,747,518	28,961,614
Amortization expense	78,486	2,402,450	457,666	508,823
Net loss (gain) on fair value change of financial assets and liabilities at fair value through profit or loss	(64,995)	(1,989,490)	2,783,902	(447,559)
Finance costs	116,571	3,568,241	1,799,494	2,261,075
Interest income	(15,231)	(466,211)	(306,871)	(230,067)
Dividend income	(6,220)	(190,397)	(59,039)	(26,411)
Compensation cost of employee share options	7,045	215,648	438,765	470,788
Share of loss (profit) of associates and joint ventures	15,689	480,244	(525,782)	(1,503,910)
Loss (gain) on disposal of property, plant and equipment	1,859	56,902	(348,070)	131,044
Impairment loss recognized on financial assets	22,072	675,624	77,101	91,886
Reversal of impairment loss recognized on financial assets				(28,022)
Impairment loss recognized on non- financial assets	36,393	1,113,998	1,113,499	1,340,011
Reversal of impairment loss recognized on non-financial assets	(3,267)	(100,000)
Gain on disposal of subsidiaries			(5,589,457)
Gain on remeasurement of investments accounted for using the equity method	(242,451)	(7,421,408)
Net loss (gain) on foreign currency exchange	44,442	1,360,380	(2,356,480)	(407,160)
Others	37,332	1,142,735	1,172,005	900,378
Financial assets held for trading			(226,049)	1,052,111
Financial assets mandatorily at fair value through profit or loss	11,288	345,540
Contract assets	(16,601)	(508,166)
Trade receivables	(304,265)	(9,313,539)	(4,066,374)	(6,184,873)
Other receivables	14,489	443,517	(330,491)	(211,755)
Inventories	(302,179)	(9,249,714)	(2,907,848)	3,156,759
Other current assets	(12,583)	(385,172)	(781,477)	(24,517)
Financial liabilities held for trading	(66,637)	(2,039,771)	(3,874,662)	(2,952,116)
Trade payables	228,331	6,989,198	4,753,270	1,665,420
Other payables	33,203	1,016,338	685,398	1,380,205
Other current liabilities	7,455	228,190	211,145	(2,347,599)
Other operating activities items	(9,204)	(281,736)	27,538	(407,143)
Cash generated from operations	1,970,517	60,317,532	51,915,364	55,117,687
Interest received	17,108	523,679	236,746	228,509
Dividend received	9,731	297,882	1,929,218	4,043,644
Interest paid	(105,820)	(3,239,159)	(1,666,759)	(2,043,870)
Income tax paid	(222,974)	(6,825,243)	(4,983,769)	(5,238,103)
Net cash generated from operating activities	1,668,562	51,074,691	47,430,800	52,107,867
CASH FLOWS FROM INVESTING ACTIVITIES
Purchase of financial assets at fair value through other comprehensive income	(3,430)	(105,000)
Proceeds on sale of financial assets at fair value through other comprehensive income	3,078	94,217
Return of capital from financial assets at fair value through other comprehensive income	3,799	116,278
Purchase of financial assets designated as at fair value through profit or loss			(61,308,095)	(64,853,336)
Proceeds on sale of financial assets designated as at fair value through profit or loss			61,601,865	66,472,870
Purchase of available-for-sale financial assets			(902,648)	(1,590,928)
Proceeds on sale of available-for-sale financial assets			1,121,517	867,336
Cash received from return of capital by available-for-sale financial assets			16,175	28,927
Acquisition of associates and joint ventures	(14,752)	(451,563)		(16,041,463)
Net cash outflow on acquisition of subsidiaries	(3,111,462)	(95,241,855)		(73,437)
Cash received from return of capital by investee accounted for using the equity method	8,590	262,941
Net cash inflow from disposal of subsidiaries			7,020,883
Payments for property, plant and equipment	(1,352,057)	(41,386,443)	(24,699,240)	(26,714,163)
Proceeds from disposal of property, plant and equipment	36,839	1,127,644	1,488,210	670,200
Payments for intangible assets	(18,875)	(577,765)	(337,984)	(513,893)
Proceeds from disposal of intangible assets			34,690	25,646
Payments for investment properties	(4,109)	(125,764)	(186,522)
Decrease (increase) in other financial assets	202,827	6,208,527	236,227	(1,231,186)
Increase in other non-current assets	(64,383)	(1,970,772)	(171,320)	(206,031)
Proceeds from financial liabilities for hedging	81,909	2,507,233
Net cash used in investing activities	(4,232,026)	(129,542,322)	(16,086,242)	(43,159,458)
CASH FLOWS FROM FINANCING ACTIVITIES
Net proceeds from (repayment of) short-term borrowings borrowings	729,429	22,327,813	(2,038,993)	(10,640,229)
Net repayment of short-term bills payable				(4,348,054)
Proceeds from issue of bonds			8,000,000	9,000,000
Repayment of bonds payable	(202,078)	(6,185,600)	(9,123,972)	(10,365,135)
Proceeds from long-term borrowings	6,525,436	199,743,582	35,394,158	62,282,917
Repayment of long-term borrowings	(3,731,873)	(114,232,623)	(51,867,539)	(52,924,902)
Dividends paid	(346,737)	(10,613,626)	(11,214,221)	(12,243,766)
Proceeds from issue of ordinary shares			10,290,000
Proceeds from exercise of employee share options	41,479	1,269,680	1,439,819	995,832
Payments for buy-back of ordinary shares	(2,329)	(71,302)
Proceeds from disposal of interests in subsidiaries	91,721	2,807,568
Decrease in non-controlling interests	(386,156)	(11,820,227)	(246,440)	(3,063,623)
Other financing activities items	(3,720)	(113,859)	43,761	219,940
Net cash generated from (used in) financing activities	2,715,172	83,111,406	(19,323,427)	(21,087,020)
EFFECTS OF EXCHANGE RATE CHANGES ON THE BALANCE OF CASH AND CASH EQUIVALENTS HELD IN FOREIGN CURRENCY	26,024	796,595	(4,335,589)	(4,720,046)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	177,732	5,440,370	7,685,542	(16,858,657)
CASH AND CASH EQUIVALENTS AT THE BEGINNING OF THE YEAR	1,505,327	46,078,066	38,392,524	55,251,181
CASH AND CASH EQUIVALENTS AT THE END OF THE YEAR	$ 1,683,059	$ 51,518,436	$ 46,078,066	$ 38,392,524

General Information

General Information	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
General Information	1. GENERAL INFORMATION ASE Technology Holding Co ., The board of directors of the Company’s subsidiaries, Advanced Semiconductor Engineering, Inc. (symbol “2311”, “ASE”) and Siliconware Precision Industries Co., Ltd. (symbol “2325”, “SPIL”), approved in June 2016 to enter into and execute a joint share exchange agreement to establish the Company and the Company acquired all issued and outstanding ordinary shares of ASE and SPIL in the way of share exchange. The share exchange was conducted at an exchange ratio of 1 ordinary share of ASE for 0.5 ordinary share of the Company, and at NT$51.2 in cash per SPIL’s ordinary share. The share exchange transaction has been approved both at ASE’s and SPIL’s special shareholders’ meeting on February 12, 2018 and has been completed on April 30, 2018. As a result, ASE and SPIL became wholly-owned subsidiaries of the Company on April 30, 2018, and both of ASE’s and SPIL’s ordinary shares have been delisted while the ordinary shares of the Company were listed starting from the same date under the symbol “3711”. In addition, ASE’s ordinary shares that have been traded on the New York Stock Exchange (the “NYSE”) under the symbol “ASX” in the form of American Depositary Shares (“ADS”) starting from September 2000 were exchanged as the Company’s ADSs under the same symbol “ASX” starting from April 30, 2018. For enhancing operational flexibility through organization restructure, the board of directors of ASE resolved in October 2018 to spin off its investment department which was responsible for managing the ordinary shares and assets of USI Inc. (“USIINC”) as well as relevant assets into a newly established company, USI Global Inc. (“USI Global”). USI Global then issued new ordinary shares to the Company as a consideration. In November 2018, the spin-off has been completed and the Company has obtained control over ASE and USI Global. In December 2018, the board of directors of the Company and USI Global further resolved to proceed with the merger which was completed in January 2019. After the merger, the Company is the surviving company while USI Global is the dissolving company. The aforementioned spin-off and merger have no material effect on the Group’s financial position and financial performance. The ordinary shares of the Company’s subsidiary, Universal Scientific Industrial (Shanghai) Co., Ltd. (“USISH”), have been listed on the Shanghai Stock Exchange (the “SSE”) under the symbol “601231” since February 2012. The consolidated financial statements are presented in the Company’s functional currency, New Taiwan dollar (NT$).

Approval of Financial Statement

Approval of Financial Statements	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Approval of Financial Statements	2. APPROVAL OF FINANCIAL STATEMENTS The consolidated financial statements were approved for issue by the management on April 22, 2019.

Application of New and Revised

Application of New and Revised International Financial Reporting Standards as Issued by the International Accounting Standards Board ("IASB") ( Collectively, "IFRSs")	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Application of New and Revised International Financial Reporting Standards as Issued by the International Accounting Standards Board ("IASB") ( Collectively, "IFRSs")	3. APPLICATION OF NEW AND REVISED INTERNATIONAL FINANCIAL REPORTING STANDARDS AS ISSUED BY THE INTERNATIONAL ACCOUNTING STANDARDS BOARD (“IASB”) (collectively, “IFRSs”) a. Amendments to IFRSs that are mandatorily effective for the current year In the current year, the Group has applied the following new, revised or amended standards and interpretations that have been issued and effective: New, Revised or Amended Standards and Interpretations Effective Date Issued by IASB (Note 1) Amendments to IFRS 2 Classification and Measurement of Share-based Payment Transactions January 1, 2018 IFRS 9 Financial Instruments January 1, 2018 Amendments to IFRS 9 and IFRS 7 Mandatory Effective Date of IFRS 9 and Transition Disclosures January 1, 2018 IFRS 15 Revenue from Contracts with Customers January 1, 2018 Amendments to IFRS 15 Clarifications to IFRS15 Revenue from Contracts with Customers January 1, 2018 Amendments to IAS 40 Transfers of investment property January 1, 2018 IFRIC 22 Foreign Currency Transactions and Advance Consideration January 1, 2018 Note 1: The aforementioned new, revised or amended standards and interpretations are effective for annual period beginning on or after the effective dates, unless specified otherwise. Except for the following, the initial application of the aforementioned new, revised or amended standards and interpretations did not have effect on the Group’s accounting policies. 1) IFRS 9 “Financial Instruments” and related amendments IFRS 9 supersedes IAS 39 “Financial Instruments: Recognition and Measurement”, with consequential amendments to IFRS 7 “Financial Instruments: Disclosures” and other standards. IFRS 9 sets out the requirements for classification, measurement and impairment of financial assets and hedge accounting. Refer to Note 4 for information relating to the relevant accounting policies. The requirements for classification, measurement and impairment of financial assets have been applied retrospectively from January 1, 2018, and the requirements for hedge accounting have been applied prospectively. IFRS 9 is not applicable to items that have already been derecognized as of December 31, 2017. The impact of adoption on the consolidated financial statements was not material. Classification, measurement and impairment of financial assets On the basis of the facts and circumstances that existed as of January 1, 2018, the Group has performed an assessment of the classification of recognized financial assets and has elected not to reflect the figures on a retrospective basis. The following table shows the original measurement categories and carrying amount under IAS 39 and the new measurement categories and carrying amount under IFRS 9 for each class of the Group’s financial assets and financial liabilities as of January 1, 2018. Measurement Category Carrying Amount Financial Assets IAS 39 IFRS 9 IAS 39 IAS 39 IFRS 9 IFRS 9 Remark NT$ US$ (Note 4) NT$ US$ (Note 4) Cash and cash equivalents Loans and receivables Amortized cost $ 46,078,066 $ 1,505,327 $ 46,078,066 $ 1,505,327 Derivatives Held for trading Mandatorily at fair value through profit or loss (“FVTPL”) 121,863 3,981 121,863 3,981 Equity instruments Held for trading Mandatorily at FVTPL 4,410,732 144,094 4,410,732 144,094 Available-for-sale Mandatorily at FVTPL 279,791 9,141 279,791 9,141 b) Available-for-sale Fair value through other comprehensive income (“FVTOCI”) - equity instruments 908,549 29,681 908,549 29,681 a) Open-end mutual funds Held for trading Mandatorily at FVTPL 589,976 19,274 589,976 19,274 Available-for-sale Mandatorily at FVTPL 23,825 778 23,825 778 b) Debt instruments Designated as at FVTPL Mandatorily at FVTPL 100,496 3,283 100,496 3,283 Other financial assets FVTOCI - debt instruments 1,000,000 32,669 1,080,000 35,283 d) Time deposits with original maturity of over three months, pledged time deposits and guarantee deposits Loans and receivables Amortized cost 405,520 13,248 405,520 13,248 c) Trade receivables and other receivables Loans and receivables Amortized cost 56,252,661 1,837,722 56,252,661 1,837,722 Financial Assets IAS 39 Carrying Amount as of January 1, 2018 Reclassifi- cations Remea- surements IFRS 9 Carrying Amount as of January 1, 2018 Retained Earnings Effect on January 1, 2018 Other Equity Effect on 2018 Remark NT$ NT$ NT$ NT$ NT$ NT$ FVTPL $ 5,223,067 Add: Reclassification from available-for-sale (IAS 39) - required reclassification - $ 303,616 $ - $ 110,648 $ (110,648 ) b) 5,223,067 303,616 - $ 5,526,683 110,648 (110,648 ) FVTOCI Debt instruments Add: Reclassification from other financial assets - 1,000,000 80,000 - 80,000 d) Equity instruments - 908,549 - 417,398 (417,398 ) a) - 1,908,549 80,000 1,988,549 417,398 (337,398 ) Investments accounted for using the equity method 48,753,751 - (2,586 ) 48,751,165 (163,579 ) 160,993 $ 53,976,818 $ 2,212,165 $ 77,414 $ 56,266,397 $ 364,467 $ (287,053 ) Financial Assets IAS 39 Carrying Amount as of January 1, 2018 Reclassifi- cations Remea- surements IFRS 9 Carrying Amount as of January 1, 2018 Retained Earnings Effect on January 1, 2018 Other Equity Effect on 2018 Remark US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) FVTPL $ 170,633 Add: Reclassification from available-for-sale (IAS 39) - required reclassification - $ 9,919 $ - $ 3,615 $ (3,615 ) b) 170,633 9,919 - $ 180,551 3,615 (3,615 ) FVTOCI Debt instruments Add: Reclassification from other financial assets - 32,669 2,614 - 2,614 d) Equity instruments - 29,682 - 13,636 (13,636 ) a) - 62,351 2,614 64,964 13,636 (11,022 ) Investments accounted for using the equity method 1,592,739 - (85 ) 1,592,655 (5,344 ) 5,259 $ 1,763,372 $ 72,270 $ 2,529 $ 1,838,170 $ 11,907 $ (9,378 ) a) Unquoted shares and limited partnership classified as available-for-sale are designated as at FVTOCI and the changes in fair value accumulated in other equity are transferred directly to retained earnings instead of being reclassified to profit or loss on disposal. Impairment losses previously recognized and accumulated in retained earnings are adjusted by the Group to record an increase in retained earnings and a decrease in other equity, unrealized gains or losses on financial assets at fair value through other comprehensive income, since no subsequent impairment assessment is required under IFRS 9; b) Quoted shares classified as available-for-sale are classified as at fair value through profit or loss under IFRS 9. Open-end mutual funds classified as available-for-sale are classified as at fair value through profit or loss under IFRS 9 because the contractual cash flows are not solely payments of principal and interest on the principal outstanding and they are not equity instruments. The Group reclassifies unrealized gains or losses on available-for-sale financial assets in other equity to retained earnings; c) Time deposits with original maturity of over three months, pledged time deposits and guarantee deposits are classified as measured at amortized cost under IFRS 9 because, on initial recognition, the contractual cash flows that are solely payments of principal and interest on the principal outstanding and these investments are held within a business model whose objective is to collect the contractual cash flows; and d) Debt investments with no active market are classified as at fair value through other comprehensive income under IFRS 9, because, on initial recognition, the contractual cash flows that are solely payments of principal and interest on the principal outstanding and these investments are held within a business model whose objective is achieved both by collecting contractual cash flows and selling financial assets. The Group adjusts those debt investments and other equity, unrealized gains or losses on financial assets at fair value through other comprehensive income, based on their fair value. 2) IFRS 15 “Revenue from Contracts with Customers” and related amendment IFRS 15 establishes principles for recognizing revenue that apply to all contracts with customers, and supersedes IAS 18 “Revenue”, IAS 11 “Construction Contracts” and a number of revenue-related interpretations. Refer to Note 4 for related accounting policies. Most of revenues generated from the goods manufactured by the Group’s operating segments in packaging and testing are changed to be recognized over time after the application of IFRS 15. Prior to the application of IFRS 15, the Group recognized revenues when the significant risks and rewards of ownership of inventories have been transferred to customers. The Group elected only to retrospectively apply IFRS 15 to contracts that were not complete as of January 1, 2018 and recognized the cumulative effect of retrospectively applying IFRS 15 in retained earnings on January 1, 2018. The impact of adoption on the consolidated financial statements was not material. The impact on assets, liabilities and equity as of January 1, 2018 from the initial application of IFRS 15 is set out below: IAS 18 Carrying Amount as of January 1, 2018 Adjustments Arising from Initial Application IFRS 15 Carrying Amount as of January 1, 2018 NT$ NT$ NT$ Inventories $ 24,260,911 $ (1,381,778 ) $ 22,879,133 Contract assets - current - 1,971,107 1,971,107 Investments accounted for using the equity method 48,753,751 40,139 48,793,890 Deferred tax assets 4,001,821 (7,287 ) 3,994,534 Total effect on assets $ 77,016,483 $ 622,181 $ 77,638,664 Current tax liabilities $ 7,619,328 $ 5,078 $ 7,624,406 Deferred tax liabilities 4,961,487 90,071 5,051,558 Total effect on liabilities $ 12,580,815 $ 95,149 $ 12,675,964 Retained earnings $ 73,718,545 $ 521,849 $ 74,240,394 Non-controlling interests 13,190,129 5,183 13,195,312 Total effect on equity $ 86,908,674 $ 527,032 $ 87,435,706 IAS 18 Carrying Amount as of January 1, 2018 Adjustments Arising from Initial Application IFRS 15 Carrying Amount as of January 1, 2018 US$ (Note 4) US$ (Note 4) US$ (Note 4) Inventories $ 792,581 $ (45,141 ) $ 747,440 Contract assets - current - 64,394 64,394 Investments accounted for using the equity method 1,592,739 1,311 1,594,050 IAS 18 Carrying Amount as of January 1, 2018 Adjustments Arising from Initial Application IFRS 15 Carrying Amount as of January 1, 2018 US$ (Note 4) US$ (Note 4) US$ (Note 4) Deferred tax assets $ 130,736 $ (238 ) $ 130,498 Total effect on assets $ 2,516,056 $ 20,326 $ 2,536,382 Current tax liabilities $ 248,916 $ 166 $ 249,082 Deferred tax liabilities 162,087 2,943 165,030 Total effect on liabilities $ 411,003 $ 3,109 $ 414,112 Retained earnings $ 2,408,316 $ 17,048 $ 2,425,364 Non-controlling interests 430,909 169 431,078 Total effect on equity $ 2,839,225 $ 17,217 $ 2,856,442 Had the Group applied IAS 18 in the current year, the following adjustments should have been made to reflect the line items and balances under IFRS 15. Impact on assets, liabilities and equity as of December 31, 2018 NT$ US$ (Note 4) Increase in inventories $ 2,313,269 $ 75,572 Decrease in contract assets - current (4,498,500 ) (146,961 ) Increase in trade receivables 1,073,368 35,066 Decrease in investments accounted for using the equity method (37,312 ) (1,219 ) Increase in deferred tax assets 26,389 862 Decrease in assets $ (1,122,786 ) $ (36,680 ) Decrease in current tax liabilities $ (47,028 ) $ (1,536 ) Decrease in deferred tax liabilities (141,934 ) (4,637 ) Decrease in liabilities $ (188,962 ) $ (6,173 ) Decrease in retained earnings $ (933,310 ) $ (30,490 ) Decrease in non-controlling interests (514 ) (17 ) Decrease in equity $ (933,824 ) $ (30,507 ) Impact on total comprehensive income for the year ended December 31, 2018 NT$ US$ (Note 4) Decrease in operating revenues $ (475,155 ) $ (15,523 ) Decrease in operating costs $ (101,964 ) $ (3,331 ) Increase in share of profit of associates and joint ventures $ 2,828 $ 92 Decrease in income tax expense $ (81,908 ) $ (2,676 ) Decrease in net profit and total comprehensive income for the year $ (406,792 ) $ (13,290 ) Increase (decrease) in net profit and total comprehensive income attributable to: Owners of the Company $ (411,461 ) $ (13,442 ) Non-controlling interests 4,669 152 $ (406,792 ) $ (13,290 ) Impact on earnings per share: Decrease in basic earnings per share $ (0.10 ) $ (0.00 ) Decrease in diluted earnings per share $ (0.10 ) $ (0.00 ) b. New, revised or amended standards and interpretations in issue but not yet effective The Group has not applied the following new, revised or amended standards and interpretations that have been issued but are not yet effective: New, Revised or Amended Standards and Interpretations Effective Date Issued Amendments to IFRSs Annual Improvements to IFRSs 2015-2017 Cycle January 1, 2019 Amendments to IFRS 9 Prepayment Features with Negative Compensation January 1, 2019 Amendments to IFRS 10 and IAS 28 Sale or Contribution of Assets between an Investor and its Associate or Joint Venture To be determined by IFRS 16 Leases January 1, 2019 Amendments to IAS 19 Plan Amendment, Curtailment or Settlement January 1, 2019 (Note 2) Amendments to IAS 28 Long-term Interests in Associate and Joint Venture January 1, 2019 IFRIC 23 Uncertainty over Income Tax Treatments January 1, 2019 Amendments to IFRS 3 Definition of a Business January 1, 2020 (Note 3) Amendments to IAS 1 and IAS 8 Definition of Material January 1, 2020 (Note 4) Note 1: The aforementioned new, revised or amended standards and interpretations are effective for annual period beginning on or after the effective dates, unless specified otherwise. Note 2: The Group shall apply these amendments to plan amendments, curtailments or settlements occurring on or after January 1, 2019. Note 3: The Group shall apply these amendments to business combinations for which the acquisition date is on or after the beginning of the first annual period beginning on or after January 1, 2020 and to asset acquisitions that occur on or after the beginning of that period. Note 4: The Group shall apply these amendments prospectively for annual periods beginning on or after January 1, 2020. c. Significant changes in accounting policy resulted from new, revised and amended standards and interpretations in issue but not yet effective As of the date the consolidated financial statements were authorized for issue, the Group assessed that the application of the aforementioned new, revised or amended standards and interpretations will not have material impact on the Group’s financial position and financial performance. 1) IFRS 16 “Leases” IFRS 16 sets out the accounting standards for leases that will supersede IAS 17, IFRIC 4 and a number of related interpretations. Definition of a lease Upon initial application of IFRS 16, the Group will elect to apply IFRS 16 in determining whether contracts are, or contain, a lease only to contracts entered into (or changed) on or after January 1, 2019. Contracts identified as containing a lease under IAS 17 and IFRIC 4 will not be reassessed and will be accounted for in accordance with the transitional provisions under IFRS 16. Upon initial application of IFRS 16, if the Group is a lessee, it will recognize right-of-use assets, or investment properties if the right-of-use assets meet the definition of investment properties, and lease liabilities for all leases on the consolidated balance sheets except for those whose payments under low-value asset and short-term leases will be recognized as expenses on a straight-line basis. On the consolidated statements of comprehensive income, the Group should present the depreciation expense charged on the right-of-use assets separately from the interest expense accrued on the lease liabilities; interest is computed using the effective interest method. On the consolidated statements of cash flows, cash payments for the principal portion of the lease liabilities will be classified within financing activities; cash payments for the interest portion will be classified within operating activities. The application of IFRS 16 is not expected to have a material impact on the accounting of the Group as lessor. The Group anticipates applying IFRS 16 retrospectively with the cumulative effect of the initial application of this standard recognized on January 1, 2019. Comparative information will not be adjusted on a retrospective basis. The Group expects to apply the following practical expedients: a) The Group will apply a single discount rate to a portfolio of leases with reasonably similar characteristics to measure lease liabilities. b) The Group will account for those leases for which the lease term ends on or before December 31, 2019 as short-term leases. c) The Group will exclude initial direct costs from the measurement of right-of-use assets on January 1, 2019. d) The Group will use hindsight, such as in determining lease terms, to measure lease liabilities. For leases currently classified as finance leases under IAS 17, the carrying amount of right-of-use assets and lease liabilities on January 1, 2019 will be determined as the carrying amount of the leased assets and finance lease payables as of December 31, 2018. Anticipated impact on assets, liabilities and equity as of January 1, 2019 IAS 17 Carrying Amount as of December 31, 2018 Adjustments Arising from Initial Application of IFRS 16 IFRS 16 Carrying Amount as of January 1, 2019 NT$ NT$ NT$ Other financial assets - current $ 6,539,467 $ (31 ) $ 6,539,436 Other current assets 3,773,384 (385,014 ) 3,388,370 Long-term prepayments for lease 10,764,835 (10,764,835 ) - Property, plant and equipment 214,592,588 (277,079 ) 214,315,509 Right-of-use assets - 10,724,198 10,724,198 Investment properties 7,738,379 6,599,225 14,337,604 Other financial assets - non-current 1,044,294 (2,747 ) 1,041,547 Other intangible assets 30,897,700 (59,667 ) 30,838,033 Total effect on assets $ 275,350,647 $ 5,834,050 $ 281,184,697 Obligation under leases - current $ - $ 490,085 $ 490,085 Other current liabilities 5,984,156 (17,144 ) 5,967,012 Obligation under leases - non-current - 5,598,071 5,598,071 Other current liabilities - non-current 1,371,302 (236,962 ) 1,134,340 Total effect on liabilities $ 7,355,458 $ 5,834,050 $ 13,189,508 IAS 17 Carrying Amount as of December 31, 2018 Adjustments Arising from Initial Application of IFRS 16 IFRS 16 Carrying Amount as of January 1, 2019 US$ (Note 4) US$ (Note 4) US$ (Note 4) Other financial assets - current $ 213,638 $ (1 ) $ 213,637 Other current assets 123,273 (12,578 ) 110,695 Long-term prepayments for lease 351,677 (351,677 ) - Property, plant and equipment 7,010,539 (9,052 ) 7,001,487 Right-of-use assets - 350,349 350,349 Investment properties 252,806 215,591 468,397 Other financial assets - non-current 34,116 (90 ) 34,026 Other intangible assets 1,009,399 (1,949 ) 1,007,450 Total effect on assets $ 8,995,448 $ 190,593 $ 9,168,041 Obligation under leases - current $ - $ 16,010 $ 16,010 Other current liabilities 195,497 (560 ) 194,937 Obligation under leases - non-current - 182,884 182,884 Other current liabilities - non-current 44,799 (7,741 ) 37,058 Total effect on liabilities $ 240,296 $ 190,593 $ 430,889 2) Amendments to IAS 19 “Plan Amendment, Curtailment or Settlement” The amendments stipulate that, if a plan amendment, curtailment or settlement occurs, the current service cost and the net interest for the remainder of the annual reporting period are determined using the actuarial assumptions used for the remeasurement of the net defined benefit liabilities (assets). In addition, the amendments clarify the effect of a plan amendment, curtailment or settlement on the requirements regarding the asset ceiling. The Group will apply the above amendments prospectively.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Significant Accounting Policies	4. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES a. Statement of compliance The consolidated financial statements have been prepared in accordance with IFRSs as issued by the IASB. b. Basis of preparation As disclosed in Note 1, the share exchange between the Company and ASE was an organization restructure under common control that the Company was essentially the continuation of ASE. The related assets and liabilities in the Company’s consolidated financial statements, before the date of incorporation, were recognized based on the carrying amounts of those in ASE’s consolidated financial statements. The consolidated financial statements of the Company for prior periods are prepared under the assumption that the Company owned 100% shareholdings of ASE at the very beginning. The consolidated financial statements have been prepared on the historical cost basis except for financial instruments which are measured at fair value and net defined benefit liabilities which are measured at the present value of the defined benefit obligation less the fair value of plan assets. The fair value measurements, which are grouped into Levels 1 to 3 based on the degree to which the fair value measurement inputs are observable and based on the significance of the inputs to the fair value measurement in its entirety, are described as follows: 1) Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities; 2) Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for an asset or a liability, either directly (i.e. as prices) or indirectly (i.e. derived from prices); and 3) Level 3 inputs are unobservable inputs for an asset or a liability. c. Classification of current and non-current assets and liabilities Current assets include cash and cash equivalents and those assets held primarily for trading purposes or expected to be realized within twelve months after the balance sheet date, unless the asset is to be used for an exchange or to settle a liability, or otherwise remains restricted, at more than twelve months after the balance sheet date. Current liabilities are obligations incurred for trading purposes or to be settled within twelve months after the balance sheet date (even if an agreement to refinance, or to reschedule payments, on a long-term basis is completed after the balance sheet date and before the consolidated financial statements are authorized for issue) and liabilities that do not have an unconditional right to defer settlement for at least 12 months after the balance sheet date (terms of a liability that could, at the option of the counterparty, result in its settlement by the issue of equity instruments do not affect its classification). Assets and liabilities that are not classified as current are classified as non-current. The Group engages in the construction business which has an operating cycle of over one year. The normal operating cycle applies when considering the classification of the Group’s construction-related assets and liabilities. d. Basis of consolidation 1) Principles for preparing consolidated financial statements The Company became the ultimate parent company of the Group after completing the share exchange with ASE on April 30, 2018. In addition, the Company obtained control over SPIL on April 30, 2018 and, therefore, included SPIL’s subsidiaries in the Group’s consolidated financial statements from the same date. The consolidated financial statements incorporate the financial statements of the Company and the entities controlled by the Company (i.e. its subsidiaries, including structured entities). Income and expenses of subsidiaries acquired or disposed of during the period are included in the consolidated statement of profit or loss and other comprehensive income from the effective dates of acquisitions up to the effective dates of disposals, as appropriate. When necessary, adjustments are made to the financial statements of subsidiaries to bring their accounting policies into line with those used by the Company. All intra-group transactions, balances, income and expenses are eliminated in full upon consolidation. Total comprehensive income of subsidiaries is attributed to the owners of the Company and to the non-controlling interests even if this results in the non-controlling interests having a deficit balance. Changes in the Group’s ownership interests in subsidiaries that do not result in the Group losing control over the subsidiaries are accounted for as equity transactions. The carrying amounts of the interests of the Group and the non-controlling interests are adjusted to reflect the changes in their relative interests in the subsidiaries. Any difference between the amount by which the non-controlling interests are adjusted and the fair value of the consideration paid or received is recognized directly in equity and attributed to the owners of the Company. When the Group loses control of a subsidiary, a gain or loss is recognized in profit or loss and is calculated as the difference between (i) the aggregate of the fair value of the consideration received and any investment retained in the former subsidiary at its fair value at the date when control is lost and (ii) the assets (including any goodwill) and liabilities and any non-controlling interests of the former subsidiary at their carrying amounts at the date when control is lost. The Group accounts for all amounts recognized in other comprehensive income in relation to that subsidiary on the same basis as would be required had the Group directly disposed of the related assets or liabilities. 2) Subsidiaries included in consolidated financial statements were as follows: Establishment and Percentage of Ownership (%) December 31 Name of Investee Main Businesses Operating Location 2017 2018 ASE Engaged in the packaging and testing of semiconductors Kaohsiung, R.O.C. 100.0 100.0 A.S.E. Holding Limited Holding company Bermuda 100.0 100.0 J & R Holding Limited (“J&R Holding”) Holding company Bermuda 100.0 100.0 Innosource Limited Holding company British Virgin Islands 100.0 100.0 Omniquest Industrial Limited Holding company British Virgin Islands 100.0 100.0 ASE Marketing & Service Japan Co., Ltd. Engaged in marketing and sales services Japan 100.0 100.0 ASE Test, Inc. Engaged in the testing of semiconductors Kaohsiung, R.O.C. 100.0 100.0 Luchu Development Corporation Engaged in the development of real estate properties Taipei, R.O.C. 86.1 86.1 TLJ Intertech Inc. (“TLJ”) Engaged in information software services Taipei, R.O.C. 60.0 60.0 MingFung Information Service Corp., Ltd. Engaged in information software services, and was established in May 2018. Taipei, R.O.C. - 100.0 Alto Enterprises Limited Holding company British Virgin Islands 100.0 100.0 Super Zone Holdings Limited Holding company Hong Kong 100.0 100.0 ASE (Kun Shan) Inc. Engaged in the packaging and testing of semiconductors Kun Shan, China 100.0 100.0 ASE Investment (Kun Shan) Limited Holding company Kun Shan, China 100.0 100.0 Advanced Semiconductor Engineering (China) Ltd. Will engage in the packaging and testing of semiconductors Shanghai, China 100.0 100.0 ASE Investment (Labuan) Inc. Holding company Malaysia 100.0 100.0 ASE Test Limited (“ASE Test”) Holding company Singapore 100.0 100.0 ASE (Korea) Inc. (“ASE Korea”) Engaged in the packaging and testing of semiconductors Korea 100.0 100.0 J&R Industrial Inc. Engaged in leasing equipment and investing activity Kaohsiung, R.O.C. 100.0 100.0 ASE Japan Co., Ltd. (“ASE Japan”) Engaged in the packaging and testing of semiconductors Japan 100.0 100.0 ASE (U.S.) Inc. After-sales service and sales support U.S.A. 100.0 100.0 Global Advanced Packaging Technology Limited Holding company British Cayman Islands 100.0 100.0 ASE WeiHai Inc. Engaged in the packaging and testing of semiconductors Shandong, China 100.0 100.0 Establishment and Percentage of Ownership (%) December 31 Name of Investee Main Businesses Operating Location 2017 2018 Suzhou ASEN Semiconductors Co., Ltd. (“ASEN”) Engaged in the packaging and testing of semiconductors Suzhou, China 60.0 70.0 Anstock Limited Engaged in financing activity British Cayman Islands 100.0 100.0 Anstock II Limited Engaged in financing activity British Cayman Islands 100.0 100.0 ASE (Shanghai) Inc. Engaged in the production of substrates Shanghai, China 100.0 100.0 ASE Corporation Holding company British Cayman Islands 100.0 100.0 ASE Mauritius Inc. Holding company Mauritius 100.0 100.0 ASE Labuan Inc. Holding company Malaysia 100.0 100.0 Shanghai Ding Hui Real Estate Development Co., Ltd. Engaged in the development, construction and sale of real estate properties Shanghai, China 100.0 100.0 Shanghai Ding Qi Property Management Co., Ltd. Engaged in the management of real estate properties Shanghai, China 100.0 100.0 Advanced Semiconductor Engineering (HK) Limited Engaged in the trading of substrates Hong Kong 100.0 100.0 Shanghai Ding Wei Real Estate Development Co., Ltd. Engaged in the development, construction and leasing of real estate properties Shanghai, China 100.0 100.0 Shanghai Ding Yu Real Estate Development Co., Ltd. Engaged in the development, construction and leasing of real estate properties Shanghai, China 100.0 100.0 Shanghai Ding Fan Department Store Co., Ltd. Engaged in department store business Shanghai, China 100.0 100.0 Kun Shan Ding Hong Real Estate Development Co., Ltd. Engaged in the development, construction and leasing of real estate properties Kun Shan, China 100.0 100.0 Shanghai Ding Xu Property Management Co., Ltd. Engaged in the management of real estate properties Shanghai, China 100.0 100.0 ASE Electronics Inc. Engaged in the production of substrates Kaohsiung, R.O.C. 100.0 100.0 ASE Test Holdings, Ltd. Holding company British Cayman Islands 100.0 100.0 ASE Holdings (Singapore) Pte. Ltd. Holding company Singapore 100.0 100.0 ASE Singapore Pte. Ltd. Engaged in the packaging and testing of semiconductors Singapore 100.0 100.0 ISE Labs, Inc. Engaged in the testing of semiconductors U.S.A. 100.0 100.0 ASE Electronics (M) Sdn. Bhd. Engaged in the packaging and testing of semiconductors Malaysia 100.0 100.0 ASE Assembly & Test (Shanghai) Limited Engaged in the packaging and testing of semiconductors Shanghai, China 100.0 100.0 Establishment and Percentage of Ownership (%) December 31 Name of Investee Main Businesses Operating Location 2017 2018 ASE Trading (Shanghai) Ltd. Liquidated in December 2018 Shanghai, China 100.0 - ISE Labs, China, Ltd. Engaged in the testing of semiconductors, and was established in October 2018 Shanghai, China - 100.0 Wuxi Tongzhi Microelectronics Co., Ltd. Engaged in the packaging and testing of semiconductors Wuxi, China 100.0 100.0 USI Global Engaged in investing activities, and was established in November 2018 and then dissolved in January 2019 Nantou, R.O.C. - 100.0 USIINC Engaged in investing activity Nantou, R.O.C. 99.2 100.0 Huntington Holdings International Co., Ltd. Holding company British Virgin Islands 99.2 100.0 Unitech Holdings International Co., Ltd. (“UHI”) Holding company British Virgin Islands 99.2 100.0 Real Tech Holdings Limited Holding company British Virgin Islands 99.2 100.0 Universal ABIT Holding Co., Ltd. In the process of liquidation British Cayman Islands 99.2 100.0 Rising Capital Investment Limited Holding company British Virgin Islands 99.2 100.0 Rise Accord Limited Holding company British Virgin Islands 99.2 100.0 Universal Scientific Industrial (Kunshan) Co., Ltd. Engaged in the manufacturing and sale of computer assistance system and related peripherals Kun Shan, China 99.2 100.0 USI Enterprise Limited (“USIE”) Engaged in the services of investment advisory and warehousing management Hong Kong 96.9 95.4 Universal Scientific Industrial (Shanghai) Co., Ltd. (“USISH”) Engaged in the designing, manufacturing and sale of electronic components Shanghai, China 75.8 74.6 Universal Global Technology Co., Limited Holding company Hong Kong 75.8 74.6 Universal Global Technology (Kunshan) Co., Ltd. Engaged in the designing and manufacturing of electronic components Kun Shan, China 75.8 74.6 Universal Global Technology (Shanghai) Co., Ltd. Engaged in the processing and sales of computer and communication peripherals as well as business in import and export of goods and technology Shanghai, China 75.8 74.6 Universal Global Electronics (Shanghai) Co., Ltd. Engaged in the sale of electronic components and telecommunications equipment Shanghai, China 75.8 74.6 Establishment and Percentage of Ownership (%) December 31 Name of Investee Main Businesses Operating Location 2017 2018 USI America Inc. Engaged in the manufacturing and processing of motherboards and wireless network communication and provision of related technical service U.S.A. 75.8 74.6 Universal Global Industrial Co., Limited Engaged in manufacturing, trading and investing activity Hong Kong 75.8 74.6 Universal Global Scientific Industrial Co., Ltd. (“UGTW”) Engaged in the manufacturing of components of telecomm and cars and provision of related R&D services Nantou, R.O.C. 75.8 74.6 Universal Scientific Industrial De Mexico S.A. De C.V. Engaged in the assembling of motherboards and computer components Mexico 75.8 74.6 USI Japan Co., Ltd. Engaged in the manufacturing and sale of computer peripherals, integrated chip and other related accessories Japan 75.8 74.6 USI Electronics (Shenzhen) Co., Ltd. Engaged in the design, manufacturing and sale of motherboards and computer peripherals Shenzhen, China 75.8 74.6 Universal Global Electronics Co., Ltd. Engaged in accepting and outsourcing orders as well as sales of electronic components and service of technical advisory, and was established in February 2018 Hong Kong - 74.6 Universal Scientific Industrial Co., Ltd. (“USI”) Engaged in the manufacturing, processing and sale of computers, computer peripherals and related accessories Nantou, R.O.C. 75.5 74.4 SPIL Engaged in the assembly, testing and turnkey services of integrated circuits Taichung, R.O.C. - 100.0 SPIL (B.V.I.) Holding Limited Engaged in investing activities British Virgin Islands - 100.0 Siliconware Investment Co., Ltd. Engaged in investing activities Taipei, R.O.C. - 100.0 Siliconware USA, Inc. Engaged in marketing activities U.S.A. - 100.0 Establishment and Percentage of Ownership (%) December 31 Name of Investee Main Businesses Operating Location 2017 2018 SPIL (Cayman) Holding Limited Engaged in investing activities British Cayman Islands - 100.0 Siliconware Technology (Suzhou) Limited Engaged in the packaging and testing of semiconductors Suzhou, China - 70.0 Siliconware Electronics (Fujian) Co., Limited Engaged in the packaging and testing of semiconductors Fujian, China - 100.0 e. Business combinations Acquisitions of businesses are accounted for using the acquisition method. Acquisition-related costs are generally recognized in profit or loss as they are incurred. Goodwill is measured as the excess of the sum of the consideration transferred, the amount of any non-controlling interests in the acquiree, and the fair value of the acquirer’s previously held equity interest in the acquiree (if any) over the net of the acquisition-date amounts of the identifiable assets acquired and the liabilities assumed. If, after re-assessment, the net of the acquisition-date amounts of the identifiable assets acquired and liabilities assumed exceeds the sum of the consideration transferred, the amount of any non-controlling interests in the acquiree and the fair value of the acquirer’s previously held interest in the acquiree (if any), the excess is recognized immediately in profit or loss as a bargain purchase gain. When a business combination is achieved in stages, the Group’s previously held equity interest in the acquiree is remeasured to its acquisition-date fair value and the resulting gain or loss, if any, is recognized in profit or loss or other comprehensive income. Amounts arising from interests in the acquiree prior to the acquisition date that have previously been recognized in other comprehensive income are recognized on the same basis as would be required if that interest were directly disposed of by the Group. If the initial accounting for a business combination is incomplete by the end of the reporting period in which the combination occurs, the Group reports provisional amounts for the items for which the accounting is incomplete. Those provisional amounts are adjusted retrospectively during the measurement period, or additional assets or liabilities are recognized, to reflect new information obtained about facts and circumstances that existed at the acquisition date that, if known, would have affected the amounts recognized at that date. Business combination involving entities under common control is not accounted for by acquisition method but accounted for at the carrying amounts of the entities. f. Foreign currencies In preparing the financial statements of each individual group entity, transactions in currencies other than the entity’s functional currency (i.e. foreign currencies) are recognized at the rates of exchange prevailing at the dates of the transactions. At each balance sheet date, monetary items denominated in foreign currencies are retranslated at the rates prevailing at that date. Exchange differences on monetary items arising from settlement or translation are recognized in profit or loss in the period in which they arise except for exchange differences on transactions entered into in order to hedge certain foreign currency risks. Non-monetary items measured at fair value that are denominated in foreign currencies are retranslated at the rates prevailing at the date when the fair value was determined. Exchange differences arising from the retranslation of non-monetary items are included in profit or loss for the period except for exchange differences arising from the retranslation of non-monetary items in respect of which gains and losses are recognized directly in other comprehensive income, in which cases, the exchange differences are also recognized directly in other comprehensive income. Non-monetary items that are measured at historical cost in a foreign currency are translated using the exchange rate at the date of the transaction, and are not retranslated. For the purposes of presenting the consolidated financial statements, the assets and liabilities of the Group’s foreign operations (including subsidiaries, associates and joint ventures in other countries that use currencies which are different from the currency of the Company) are translated into the New Taiwan dollars using exchange rates prevailing at each balance sheet date. Income and expense items are translated at the average exchange rates for the period. The resulting currency translation differences are recognized in other comprehensive income and accumulated in equity attributed to the owners of the Company and non-controlling interests as appropriate. On the disposal of the Group’s entire interest in a foreign operation, or a disposal involving the loss of control over a subsidiary that includes a foreign operation, or a partial disposal of an interest in a joint arrangement or an associate that includes a foreign operation of which the retained interest becomes a financial asset, all of the exchange differences accumulated in equity in respect of that operation attributable to the owners of the Company are reclassified to profit or loss. In relation to a partial disposal of a subsidiary that does not result in the Group losing control over the subsidiary, the proportionate share of accumulated exchange differences is re-attributed to the non-controlling interests of the subsidiary and is not recognized in profit or loss. For all other partial disposals, the proportionate share of the accumulated exchange differences recognized in other comprehensive income is reclassified to profit or loss. g. Inventories and inventories related to real estate business Inventories, including raw materials (materials received from customers for processing, mainly semiconductor wafers, are excluded from inventories as title and risk of loss remain with the customers), supplies, work in process, finished goods, and materials and supplies in transit are stated at the lower of cost or net realizable value. Inventory write-downs are made by item, except for those that may be appropriate to group items of similar or related inventories. Net realizable value is the estimated selling prices of inventories less all estimated costs of completion and estimated costs necessary to make the sale. Raw materials and supplies are recorded at moving average cost while work in process and finished goods are recorded at standard cost. Inventories related to real estate business include land and buildings held for sale, land held for construction and construction in progress. Land held for development is recorded as land held for construction upon obtaining the title of ownership. Prior to the completion, the borrowing costs directly attributable to construction in progress are capitalized as part of the cost of the asset. Construction in progress is transferred to land and buildings held for sale upon completion. Land and buildings held for sale, construction in progress and land held for construction are stated at the lower of cost or net realizable value and related write-downs are made by item. The amounts received in advance for real estate properties are first recorded as advance receipts and then recognized as revenue when the construction is completed and the title and significant risk of the real estate properties are transferred to customers. Cost of sales of land and buildings held for sale are recognized based on the ratio of property sold to the total property developed. h. Investments in associates and joint ventures An associate is an entity over which the Group has significant influence and that is neither a subsidiary nor an interest in a joint venture. Joint venture is a joint arrangement whereby the Group and other parties that have joint control of the arrangement have rights to the net assets of the arrangement. Under the equity method, investments in an associate and a joint venture are initially recognized at cost and adjusted thereafter to recognize the Group’s share of the profit or loss and other comprehensive income of the associate and joint venture. The Group also recognizes the changes in the Group’s share of equity of associates and joint venture. Any excess of the cost of acquisition over the Group’s share of the net fair value of the identifiable assets and liabilities of an associate or a joint venture at the date of acquisition is recognized as goodwill, which is included within the carrying amount of the investment and is not amortized. Any excess of the Group’s share of the net fair value of the identifiable assets and liabilities over the cost of acquisition after reassessment is recognized immediately in profit or loss. When the Group subscribes for additional new shares of an associate and joint venture at a percentage different from its existing ownership percentage, the resulting carrying amount of the investment differs from the amount of the Group’s proportionate interest in the associate and joint venture. The Group records such a difference as an adjustment to investments with the corresponding amount charged or credited to capital surplus - changes in capital surplus from investments in associates and joint ventures accounted for using the equity method. If the Group’s ownership interest is reduced due to its additional subscription of the new shares of the associate and joint venture, the proportionate amount of the gains or losses previously recognized in other comprehensive income in relation to that associate and joint venture is reclassified to profit or loss on the same basis as would be required had the investee directly disposed of the related assets or liabilities. When the adjustment should be debited to capital surplus, but the capital surplus recognized from investments accounted for using the equity method is insufficient, the shortage is debited to retained earnings. When the Group’s share of losses of an associate and a joint venture equals or exceeds its interest in that associate and joint venture (which includes any carrying amount of the investment accounted for using the equity method and long-term interests that, in substance, form part of the Group’s net investment in the associate and joint venture), the Group discontinues recognizing its share of further losses. Additional losses and liabilities are recognized only to the extent that the Group has incurred legal obligations or constructive obligations, or made payments on behalf of that associate and joint venture. The entire carrying amount of an investment (including goodwill) is tested for impairment as a single asset by comparing its recoverable amount with its carrying amount. Any impairment loss recognized is not allocated to any asset, including goodwill, that forms part of the carrying amount of the investment. Any reversal of that impairment loss is recognized to the extent that the recoverable amount of the investment subsequently increases. The Group discontinues the use of the equity method from the date on which its investment ceases to be an associate and a joint venture. Any retained investment is measured at fair value at that date, and the fair value is regarded as the investment’s fair value on initial recognition as a financial asset. The difference between the previous carrying amount of the associate and the joint venture attributable to the retained interest and its fair value is included in the determination of the gain or loss on disposal of the associate and the joint venture. The Group accounts for all amounts previously recognized in other comprehensive income in relation to that associate and joint venture on the same basis as would be required had that associate directly disposed of the related assets or liabilities. If an investment in an associate becomes an investment in a joint venture or an investment in a joint venture becomes an investment in an associate, the Group continues to apply the equity method and does not remeasure the retained interest. When a group entity transacts with its associate and joint venture, profits and losses resulting from the transactions with the associate and joint venture are recognized in the Group’ consolidated financial statements only to the extent that interests in the associate and the joint venture are not related to the Group. i. Property, plant and equipment Except for land which is stated at cost, property, plant and equipment (including assets held under finance leases) are stated at cost less accumulated depreciation and accumulated impairment. Properties in the course of construction are carried at cost, less any recognized impairment loss. Cost includes professional fees and borrowing costs eligible for capitalization. Such assets are depreciated and classified to the appropriate categories of property, plant and equipment when completed and ready for their intended use. Freehold land is not depreciated. Depreciation of property, plant and equipment is recognized using the straight-line method. Each significant part is depreciated separately. If the lease term is shorter than the assets’ useful lives, such assets are depreciated over the lease term. The estimated useful lives, residual values and depreciation method are reviewed at each balance sheet date, with the effect of any changes in estimate accounted for on a prospective basis. On derecognition of an item of property, plant and equipment, the difference between the sales proceeds and the carrying amount of the asset is recognized in profit or loss. j. Investment properties Investment properties are properties held to earn rentals and/or for capital appreciation (including property under construction for such purposes). Investment properties also include land held for a currently undetermined future use. Investment properties are measured initially at cost, including transaction costs. Subsequent to initial recognition, investment properties are measured at cost less accumulated depreciation and accumulated impairment loss. Depreciation is recognized using the straight-line method. Investment properties under construction are stated at cost less accumulated depreciation and accumulated impairment loss. Cost includes professional fees and borrowing costs eligible for capitalization. Depreciation of these assets commences when the assets are ready for their intended use. For a transfer from property, plant and equipment to investment properties, the property’s deemed cost for subsequent accounting is its carrying amount at the end of owner-occupation. For a transfer from inventories to investment properties, the property’s deemed cost for subsequent accounting is its carrying amount at inception of an operating lease. On derecognition of an investment property, the difference between the net disposal proceeds and the carrying amount of the asset is included in profit or loss. k. Goodwill Goodwill arising from an acquisition of a business is carried at cost as established at the date of acquisition of the business less accumulated impairment loss. For the purposes of impairment testing, goodwill is allocated to each of the Group’s cash-generating units or groups of cash-generating units (referred to as “cash-generating units”) that is expected to benefit from the synergies of the combination. A cash-generating unit to which goodwill has been allocated is tested for impairment annually, or more frequently when there is an indication that the unit may be impaired, by comparing its carrying amount, including the attributed goodwill, with its recoverable amount. However, if the goodwill allocated to a cash-generating unit was acquired in a business combination during the current annual period, that unit shall be tested for impairment before the end of the current annual period. If the recoverable amount of the cash-generating unit is less than its carrying amount, the impairment loss is allocated first to reduce the carrying amount of any goodwill allocated to the unit and then pro rata to the other assets of the unit based on the carrying amount of each asset in the unit. Any impairment loss is recognized directly in profit or loss. An impairment loss recognized for goodwill is not reversed in subsequent periods. l. Other intangible assets Other intangible assets with finite useful lives acquired separately are initially measured at cost and subsequently measured at cost less accumulated amortization and accumulated impairment loss. Other intangible assets are amortized using the straight-line method over their estimated useful lives. The estimated useful lives, residual values, and amortization methods are reviewed at each balance sheet date, with the effect of any changes in estimate being accounted for on a prospective basis. Other intangible assets acquired in a business combination and recognized separately from goodwill are initially recognized at their fair value at the acquisition date which is regarded as their cost. Subsequent to initial recognition, they are measured on the same basis as intangible assets that are acquired separately. On derecognition of an intangible asset, the difference between the net disposal proceeds and the carrying amount of the asset are recognized in profit or loss. m. Impairment of tangible and intangible assets other than goodwill At each balance sheet date, the Group reviews the carrying amounts of its tangible and intangible assets, excluding goodwill, to determine whether there is any indication that those assets have suffered an impairment loss. If any such indication exists, the recoverable amount of the asset is estimated in order to determine the extent of the impairment loss. When it is not possible to estimate the recoverable amount of an individual asset, the Group estimates the recoverable amount of the cash-generating unit to which the asset belongs. Corporate assets are allocated to the individual cash-generating units on a reasonable and consistent basis of allocation. The recoverable amount is the higher of fair value less costs to sell and value in use. If the recoverable amount of an asset or cash-generating unit is estimated to be less than its carrying amount, the carrying amount of the asset or cash-generating unit is reduced to its recoverable amount, with the resulting impairment loss recognized in profit or loss. When an impairment loss

Critical Accounting Judgments a

Critical Accounting Judgments and Key Sources of Estimation Uncertainty	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Critical Accounting Judgments and Key Sources of Estimation Uncertainty	5. CRITICAL ACCOUNTING JUDGMENTS AND KEY SOURCES OF ESTIMATION UNCERTAINTY In the application of the Group’s accounting policies, which are described in Note 4, management is required to make judgments, estimates and assumptions about the carrying amounts of assets and liabilities that are not readily apparent from other sources. The estimates and underlying assumptions are based on historical experience and other factors that are considered to be relevant. Actual results may differ from these estimates. The estimates and underlying assumptions are reviewed on an ongoing basis. Revisions to accounting estimates are recognized in the period in which the estimate is revised if the revision affects only that period, or in the period of the revision and future periods if the revision affects both current and future periods. Acquisition of subsidiaries After the acquisition of a subsidiary, the Group should identify the difference between the investment cost and the Group’ share of the net fair value of the subsidiary’s identifiable assets acquired and liabilities assumed. It involves critical judgments and estimations when determining the aforementioned net fair values. The management engaged independent external appraiser to assist them in identifying and evaluating the subsidiary’s identifiable tangible assets, intangible assets and liabilities, including the type of intangible assets that may be identified and the related estimated cash flows or the relief from expenses. The excess of the fair value over the carrying amount of those identified tangible and intangible assets on the acquisition date will be depreciated or amortized over their remaining useful lives or expected future economic benefit lives. The management considered that the related estimation and assumption has appropriately reflected the net fair value of those identifiable assets acquired and liabilities assumed. However, there may be of high uncertainty related to the semiconductor industry varied by economic trends.

Cash and Cash Equivalents

Cash and Cash Equivalents	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Cash and Cash Equivalents	6. CASH AND CASH EQUIVALENTS December 31 2017 2018 NT$ NT$ US$ (Note 4) Cash on hand $ 8,404 $ 7,940 $ 259 Checking accounts and demand deposits 39,697,319 32,329,820 1,056,185 Cash equivalents 6,372,343 19,180,676 626,615 $ 46,078,066 $ 51,518,436 $ 1,683,059

Financial Instruments at Fair V

Financial Instruments at Fair Value Through Profit or Loss	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Financial Instruments at Fair Value Through Profit or Loss	7. FINANCIAL INSTRUMENTS AT FAIR VALUE THROUGH PROFIT OR LOSS December 31 2017 2018 NT$ NT$ US$ (Note 4) Financial assets designated as at FVTPL Private-placement convertible bonds $ 100,496 $ - $ - Financial assets held for trading Quoted ordinary shares $ 4,410,732 $ - $ - Open-end mutual funds 589,976 - - Forward exchange contracts 61,325 - - Swap contracts 60,538 - - 5,122,571 - - Financial assets mandatorily classified as at FVTPL Derivative instruments (non-designated hedges) Swap contracts - 1,557,714 50,889 Forward exchange contracts - 32,070 1,048 Non-derivative financial assets Quoted ordinary shares - 5,151,255 168,287 Open-end mutual funds - 581,800 19,007 Unquoted preferred shares - 275,000 8,984 Private-placement funds - 200,123 6,537 Hybrid financial assets Private-placement convertible bonds - 100,496 3,283 - 7,898,458 258,035 5,223,067 7,898,458 258,035 Current 5,223,067 7,262,227 237,250 Non-current $ - $ 636,231 $ 20,785 December 31 2017 2018 NT$ NT$ US$ (Note 4) Financial liabilities held for trading Derivative instruments (non-designated hedging) Swap contracts $ 652,107 $ 29,058 $ 949 Forward exchange contracts 25,323 7,597 248 $ 677,430 $ 36,655 $ 1,197 The Group’s private-placement convertible bonds included embedded derivative instruments which were not closely related to the host contracts and the contracts were designated as at FVTPL on initial recognition under IAS 39. After application of IFRS 9, the entire contracts are assessed and classified mandatorily as at FVTPL since they contain host contracts that are assets within the scope of IFRS 9. At each balance sheet date, the outstanding swap contracts not accounted for hedge accounting were as follows: Notional Amount Currency Maturity Period (In Thousands) December 31, 2017 Sell NT$/Buy US$ 2018.01-2018.12 NT$53,136,302/US$1,782,400 Sell US$/Buy CNY 2018.01 US$52,948/CNY349,800 Sell US$/Buy JPY 2018.02-2018.03 US$70,324/JPY7,870,000 Sell US$/Buy NT$ 2018.01 US$217,300/NT$6,505,767 December 31, 2018 Sell NT$/Buy US$ 2019.01-2019.12 NT$49,570,469/US$1,687,400 Sell US$/Buy CNY 2019.01 US$50,292/CNY349,800 Sell US$/Buy JPY 2019.01 US$54,203/JPY6,090,000 Sell US$/Buy NT$ 2019.01 US$208,800/NT$6,423,242 At each balance sheet date, the outstanding forward exchange contracts not accounted for hedge accounting were as follows: Notional Amount Currency Maturity Period (In Thousands) December 31, 2017 Sell NT$/Buy US$ 2018.01 NT$2,389,620/US$80,000 Sell US$/Buy CNY 2018.01-2018.04 US$125,000/CNY828,858 Sell US$/Buy EUR 2018.01 US$10,674/EUR9,000 Sell US$/Buy JPY 2018.01-2018.02 US$45,517/JPY5,111,101 Sell US$/Buy MYR 2018.01-2018.03 US$15,000/MYR61,859 Sell US$/Buy NT$ 2018.01 US$1,000/NT$30,142 Sell US$/Buy SGD 2018.01-2018.02 US$11,300/SGD15,305 Notional Amount December 31, 2018 Maturity Period (In Thousands) Sell NT$/Buy US$ 2019.01-2019.02 NT$2,453,540/US$80,000 Sell US$/Buy CNY 2019.01 US$29,000/CNY200,108 Sell US$/Buy EUR 2019.01 US$4,103/EUR3,600 Sell US$/Buy JPY 2019.01-2019.02 US$37,733/JPY4,231,754 Sell US$/Buy MYR 2019.01-2019.02 US$14,000/MYR58,430 Sell US$/Buy SGD 2019.01-2019.02 US$13,400/SGD18,391

Financial Assets at Fair Value

Financial Assets at Fair Value Through Other Comprehensive Income - 2018	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Financial Assets at Fair Value Through Other Comprehensive Income - 2018	8. FINANCIAL ASSETS AT FAIR VALUE THROUGH OTHER COMPREHENSIVE INCOME - 2018 December 31, 2018 NT$ US$ (Note 4) Investments in equity instruments at FVTOCI $ 580,399 $ 18,961 Investments in debt instruments at FVTOCI 1,016,924 33,222 $ 1,597,323 $ 52,183 a. Investments in equity instruments at FVTOCI December 31, 2018 NT$ US$ (Note 4) Unquoted ordinary shares $ 532,047 $ 17,381 Limited partnership 39,669 1,296 Unquoted preferred shares 8,683 284 $ 580,399 $ 18,961 Investments in equity instruments were classified as available-for-sale under IAS 39. Refer to Notes 3 and 10 for information relating to their reclassification and comparative information for prior periods. b. Investments in debt instruments at FVTOCI December 31, 2018 NT$ US$ (Note 4) Unsecured subordinate corporate bonds $ 1,016,924 $ 33,222 In June 2016, the Group acquired 1,000 units of perpetual unsecured subordinate corporate bonds in the amount of NT$1,000,000 thousand. The corporate bonds are all in denomination of NT$1,000 thousand with annual interest rate at 3.5% and with effective interest rate at 3.2% as of December 31, 2017 and 2018. The bonds were classified as other financial assets －

Credit Risk Management for Inve

Credit Risk Management for Investments in Debt Instruments - 2018	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Credit Risk Management for Investments in Debt Instruments - 2018	9. CREDIT RISK MANAGEMENT FOR INVESTMENTS IN DEBT INSTRUMENTS- 2018 The Group’s investment in unsecured subordinate corporate bonds is rated the equivalent of investment grade or higher and has low credit risk for the purpose of impairment assessment. There was no significant increase in credit risk of such debt instrument since initial recognition leading to changes in interest rates and terms, and there was also no significant change in bond issuer’s operation affecting the ability performing debt obligation. We evaluated that no expected credit losses existed. The Group reviews changes in bond yields and other public information periodically and makes an assessment whether there has been a significant increase in lifetime ECL since initial recognition.

Available-for-sale Financial As

Available-for-sale Financial Assets - 2017	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Available-for-sale Financial Assets - 2017	10. AVAILABLE-FOR-SALE FINANCIAL ASSETS - 2017 December 31, 2017 NT$ Unquoted ordinary shares $ 605,110 Quoted ordinary shares 279,791 Limited partnership 246,072 Unquoted preferred shares 57,367 Open-end mutual funds 23,825 1,212,165 Current 89,159 Non-current $ 1,123,006

Trade Receivables, Net

Trade Receivables, Net	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Trade Receivables, Net	11. TRADE RECEIVABLES, NET December 31 2017 2018 NT$ NT$ US$ (Note 4) At amortized cost Gross carrying amount $ 55,265,607 $ 79,636,748 $ 2,601,658 Less: Allowance for impairment loss 64,901 155,389 5,077 $ 55,200,706 $ 79,481,359 $ 2,596,581 a. For the year ended December 31, 2018 The Group’s average credit terms were 30 to 90 days. The Group evaluates the risk and probability of credit loss by reference to the Group’s past experiences, financial condition of each customer, as well as general economic conditions, competitive advantage and future development of the industry in which the customer operates. The Group then reviews the recoverable amount of each individual trade receivable at each balance sheet date to ensure that adequate allowance is made for possible irrecoverable amounts. In this regard, management believes the Group’s credit risk was significantly reduced. In addition, the Group applies the simplified approach to providing for expected credit losses prescribed by IFRS 9, which permits the use of lifetime expected loss provision for all trade receivables. The expected credit losses on trade receivables are estimated using a provision matrix by reference to past default experience of the debtor and an analysis of the debtor’s current financial position, adjusted for general economic conditions of the industry in which the debtors operate and an assessment of both the current as well as the forecast direction of economic conditions at each balance sheet date. The Group writes off a trade receivable when there is information indicating that the debtor is in severe financial difficulty and there is no realistic prospect of recovery. For trade receivables that have been written off, the Group continues to engage in enforcement activity to attempt to recover the receivables due. Where recoveries are made, these are recognized in profit or loss. The following table details the loss allowance of trade receivables based on the Group’s provision matrix. December 31, 2018 Not Past Due Overdue 1 to 30 days Overdue 31 to 90 Days Overdue Over 91 Days Individually Total NT$ NT$ NT$ NT$ NT$ NT$ Expected credit loss rate 0 % 0~10% 0~50% 1~100% 0~100% - Gross carrying amount $ 71,819,583 $ 6,537,819 $ 778,799 $ 405,707 $ 94,840 $ 79,636,748 Loss allowance (Lifetime ECL) (7,119 ) (4,463 ) (14,949 ) (40,080 ) (88,778 ) (155,389 ) Amortized cost $ 71,812,464 $ 6,533,356 $ 763,850 $ 365,627 $ 6,062 $ 79,481,359 Not Past Due Overdue 1 to 30 days Overdue 31 to 90 Days Overdue Over 91 Days Individually Total US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) Expected credit loss rate 0 % 0~10% 0~50% 1~100% 0~100% - Gross carrying amount $ 2,346,278 $ 213,585 $ 25,443 $ 13,254 $ 3,098 $ 2,601,658 Loss allowance (Lifetime ECL) (233 ) (147 ) (488 ) (1,309 ) (2,900 ) (5,077 ) Amortized cost $ 2,346,045 $ 213,438 $ 24,955 $ 11,945 $ 198 $ 2,596,581 The movements of the loss allowance of trade receivables were as follows: For the Year Ended December 31, 2018 NT$ US$ (Note 4) Balance at January 1, 2018 $ 64,901 $ 2,120 Net remeasurement of loss allowance 150,128 4,905 Acquisition through business combinations 3,482 114 Amounts written off (60,109 ) (1,964 ) Effects of foreign currency exchange differences (3,013 ) (98 ) Balance at December 31, 2018 $ 155,389 $ 5,077 b. For the year ended December 31, 2017 The credit term that ASE and its subsidiaries applied in 2017 was identical with that applied by the Group in 2018. Allowance for doubtful debts is assessed by reference to the collectability of receivables by evaluating the account aging, historical experience and current financial condition of customers. Aging of receivables based on the past due date December 31, 2017 NT$ Not past due $ 49,599,512 1 to 30 days 4,986,491 31 to 90 days 562,200 More than 91 days 117,404 $ 55,265,607 Aging of receivables that were past due but not impaired December 31, 2017 NT$ 1 to 30 days $ 4,942,677 31 to 90 days 378,526 $ 5,321,203 Except for those impaired, ASE and its subsidiaries had not provided an allowance for doubtful debts on trade receivables at each balance sheet date since there has not been a significant change in credit quality and the amounts were still considered collectible. ASE and its subsidiaries did not hold any collateral or other credit enhancements over these balances nor did it have a legal right to offset against any amounts owed by ASE and its subsidiaries to counterparties. Movement of the allowance for doubtful trade receivables Impaired Individually Impaired Collectively Total NT$ NT$ NT$ Balance at January 1, 2016 $ 39,046 $ 43,860 $ 82,906 Impairment losses reversed (21,501 ) (6,521 ) (28,022 ) Effect of foreign currency exchange differences (1,092 ) (83 ) (1,175 ) Balance at December 31, 2016 16,453 37,256 53,709 Impairment losses recognized 9,527 4,102 13,629 Amounts written off - (34 ) (34 ) Effect of foreign currency exchange differences (850 ) (1,553 ) (2,403 ) Balance at December 31, 2017 $ 25,130 $ 39,771 $ 64,901

Inventories

Inventories	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Inventories	12. INVENTORIES December 31 2017 2018 NT$ NT$ US$ (Note 4) Finished goods $ 6,740,816 $ 7,680,083 $ 250,901 Work in process 3,452,332 3,195,478 104,393 Raw materials 12,625,502 23,250,801 759,582 Supplies 894,196 1,892,194 61,816 Raw materials and supplies in transit 548,065 608,895 19,892 $ 24,260,911 $ 36,627,451 $ 1,196,584 The cost of inventories recognized as operating costs for the years ended December 31, 2016, 2017 and 2018 were NT$219,630,270 thousand, NT$237,193,286 thousand and NT$309,020,850 thousand (US$10,095,421 thousand), respectively, which included write-downs of inventories at NT$451,780 thousand, NT$398,824 thousand and NT$980,927 thousand (US$32,046 thousand), respectively.

Inventories Related to Real Est

Inventories Related to Real Estate Business	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Inventories Related to Real Estate Business	13. INVENTORIES RELATED TO REAL ESTATE BUSINESS December 31 2017 2018 NT$ NT$ US$ (Note 4) Land and buildings held for sale $ 25,825 $ 20,734 $ 677 Construction in progress 8,106,166 8,252,348 269,597 Land held for construction 1,687,525 1,787,526 58,397 $ 9,819,516 $ 10,060,608 $ 328,671 Construction in progress is mainly located on Hutai Road in Shanghai, China and Lidu Road in Kun Shan, China. The capitalized borrowing costs for the years ended December 31, 2016, 2017 and 2018 are disclosed in Note 26. Construction in progress located on Caobao Road in Shanghai, China was completed in the third quarter of 2017 and immediately leased out for the lease business. As a result, the Group reclassified those buildings and land use right under the line item of inventories related to real estate business to investment properties of NT$6,971,372 thousand and long-term prepayments for lease of NT$5,798,449 thousand, respectively. As of December 31, 2017 and 2018, inventories related to real estate business of NT$9,818,869 thousand and NT$10,060,608 thousand (US$328,671 thousand), respectively, are expected to be recovered longer than twelve months. Refer to Note 38 for the carrying amount of inventories related to real estate business that had been pledged by the Group to secure bank borrowings.

Other Financial Assets

Other Financial Assets	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Other Financial Assets	14. OTHER FINANCIAL ASSETS December 31 2017 2018 NT$ NT$ US$ (Note 4) Time deposits with original maturity of over three months $ 405,520 $ 6,320,669 $ 206,490 Guarantee deposits 170,594 766,190 25,031 Pledged time deposits (Note 38) 59,456 496,847 16,231 Unsecured subordinate corporate bonds (Notes 8 and 9) 1,000,000 - - Others (Note 38) 7,270 55 2 1,642,840 7,583,761 247,754 Current 472,340 6,539,467 213,638 Non-current $ 1,170,500 $ 1,044,294 $ 34,116

Investments Accounted for Using

Investments Accounted for Using the Equity Method	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Investments Accounted for Using the Equity Method	15. INVESTMENTS ACCOUNTED FOR USING THE EQUITY METHOD December 31 2017 2018 NT$ NT$ US$ (Note 4) Investments in associates $ 48,267,237 $ 9,131,814 $ 298,328 Investments in joint venture 486,514 180,494 5,896 $ 48,753,751 $ 9,312,308 $ 304,224 a. Investments in associates 1) Investments in associates accounted for using the equity method consisted of the following: Carrying Amount as of December 31 2017 2018 Operating NT$ NT$ US$ (Note 4) Name of Associate Main Business Location Material associate SPIL Engaged in the assembly, testing and turnkey services of integrated circuits R.O.C. $ 45,210,371 $ - $ - Associates that are not individually material Deca Technologies Inc. （ ） Holding company and the group engaged in manufacturing, development and marketing of wafer level packaging and interconnect technology British Cayman Islands 1,583,124 866,312 28,302 Hung Ching Development & Construction Co. (“HC”) Engaged in the development, construction and leasing of real estate properties R.O.C. 1,248,711 1,095,233 35,780 Carrying Amount as of December 31 2017 2018 Operating NT$ NT$ US$ (Note 4) Name of Associate Main Business Location Hung Ching Kwan Co. (“HCK”) Engaged in the leasing of real estate properties R.O.C. $ 309,630 $ 295,772 $ 9,663 Advanced Microelectronic Products Inc. (“AMPI”) Engaged in integrated circuit R.O.C. 215,550 184,134 6,015 ChipMOS Technologies Inc. (“ChipMOS”) Engaged in the packaging and testing of semiconductors R.O.C. - 4,237,982 138,451 Yann Yuan Investment Co., Ltd. (“Yann Yuan”) Engaged in investing activities R.O.C. - 2,752,530 89,923 48,567,386 9,431,963 308,134 Less: Deferred gain on transfer of land 300,149 300,149 9,806 $ 48,267,237 $ 9,131,814 $ 298,328 2) At each balance sheet date, the percentages of ownership held by the Group were as follows: December 31 2017 2018 SPIL 33.29 % - DECA 22.04 % 22.04 % HC 26.22 % 26.22 % HCK 27.31 % 27.31 % AMPI 38.76 % 38.76 % ChipMOS - 20.47 % Yann Yuan - 32.21 % As disclosed in Note 1, the Company acquired all issued and outstanding ordinary shares of SPIL on April 30, 2018 (the acquisition date) in accordance with the joint share exchange agreement and had the control over SPIL. The investment in SPIL originally accounted for using the equity method was remeasured to the fair value at the acquisition date. The gain arising on remeasurement of NT$7,421,408 thousand (US$ 242,451 thousand) was recognized under the line item of other gains, net (Note 26) in the consolidated statements of comprehensive income for the year ended December 31, 2018. Following the acquisition of 100% shareholdings of SPIL on April 30, 2018, the Company indirectly held ordinary shares of ChipMOS and Yann Yuan through SPIL. In June 2018, SPIL, acquired additional 19,159 thousand ordinary shares of ChipMOS from open market with total cash consideration of NT$451,563 thousand (US$14,752 thousand). As a result, the percentage of ownership in ChipMOS was increased from 18.23% to 20.47% and the SPIL had significant influence over ChipMOS. As of December 31, 2018, the Group has completed the identification of the difference between the cost of the investment and the Group’ share of the net fair value of ChipMOS’ identifiable assets and liabilities. The Group evaluated the recoverable amount of its investment in DECA by the present value of cash flow projection made by DECA’s management with discount rate of 14.1%. The recoverable amount was lower than its carrying amount and, therefore, the Group recognized an impairment loss of NT$521,010 thousand (US$17,021 thousand) under the line item of other gains, net in the consolidated statements of comprehensive income for the year ended December 31, 2018 (Note 26). 3) Fair values (Level 1 inputs in terms of IFRS 13) of investments in associates with available published price quotation are summarized as follows: December 31 2017 2018 NT$ NT$ US$ (Note 4) SPIL $ 52,176,190 $ - $ - HC $ 1,695,156 $ 1,537,307 $ 50,222 AMPI $ 468,572 $ 369,925 $ 12,085 ChipMOS $ - $ 3,886,561 $ 126,970 4) Summarized financial information in respect of the Group’s material associate The summarized financial information below represents amounts shown in SPIL’s consolidated financial statements prepared in accordance with IFRSs and adjusted by the Group for equity method accounting purposes. December 31, 2017 NT$ Current assets $ 49,065,912 Non-current assets 101,693,417 Current liabilities (26,194,615 ) Non-current liabilities (27,213,266 ) Equity $ 97,351,448 Proportion of the Group’s ownership interest in SPIL 33.29 % Net assets attributable to the Group $ 32,408,297 Goodwill 12,802,074 Carrying amount $ 45,210,371 For the Year Ended December 31, 2016 For the Year Ended December 31, 2017 For the Period from January 1, 2018 through April 29, 2018 NT$ NT$ NT$ US$ (Note 4) Operating revenue $ 85,111,913 $ 83,554,385 $ 26,169,040 $ 854,918 Gross profit $ 15,027,247 $ 12,464,792 $ 4,421,493 $ 144,446 Profit before income tax $ 7,351,661 $ 4,347,810 $ 848,072 $ 27,706 Net profit $ 5,484,462 $ 2,822,231 $ 413,317 $ 13,503 Other comprehensive income (loss) (2,373,532 ) 579,057 633,879 20,708 Total comprehensive income $ 3,110,930 $ 3,401,288 $ 1,047,196 $ 34,211 Cash dividends received from SPIL $ 3,941,740 $ 1,815,275 $ - $ - 5) Aggregate information of associates that are not individually material For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) The Group’s share of: Net profit (loss) $ (139,366 ) $ (190,532 ) $ 147,535 $ 4,820 Other comprehensive income (loss) (115,650 ) 59,676 (613,471 ) (20,042 ) Total comprehensive loss $ (255,016 ) $ (130,856 ) $ (465,936 ) $ (15,222 ) b. Investments in joint venture 1) The joint venture that was not individually material and accounted for using the equity method was the Group’s investment in ASE Embedded Electronics Inc. (“ASEEE”). As of December 31, 2017 and 2018, the percentages of ownership were both 51%. ASEEE is located in R.O.C. and engaged in the production of embedded substrate. 2) ASE’s board of directors resolved in February 2019 to purchase ordinary shares newly issued by ASEEE at par value through its capital increase by cash. The total consideration will not be more than NT$1,500,000 thousand (US$49,004 thousand), representing 150,000 thousand ordinary shares. 3) Aggregate information of the Group’s joint venture that is not individually material For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) The Group’s share of net loss and total comprehensive loss $ (90,478 ) $ (184,366 ) $ (306,156 ) $ (10,002 )

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Property, Plant and Equipment	16. PROPERTY, PLANT AND EQUIPMENT The carrying amounts of each class of property, plant and equipment were as follows: December 31 2017 2018 NT$ NT$ US$ (Note 4) Land $ 3,258,518 $ 10,165,969 $ 332,113 Buildings and improvements 58,272,864 78,963,937 2,579,678 Machinery and equipment 66,185,198 108,087,970 3,531,133 Other equipment 1,588,113 6,463,160 211,145 Construction in progress and machinery in transit 5,863,713 10,911,552 356,470 $ 135,168,406 $ 214,592,588 $ 7,010,539 For the year ended December 31, 2016 Land Buildings and improvements Machinery and equipment Other equipment Construction in progress and machinery in transit Total NT$ NT$ NT$ NT$ NT$ NT$ Cost Balance at January 1, 2016 $ 3,381,300 $ 94,447,932 $ 243,283,607 $ 7,722,408 $ 6,397,760 $ 355,233,007 Additions - 22,341 94,480 470,901 27,093,140 27,680,862 Disposals - (684,698 ) (5,956,179 ) (159,822 ) (268,782 ) (7,069,481 ) Reclassification - 5,110,102 19,661,732 691,276 (25,463,285 ) (175 ) Acquisitions through business combinations - - - 1,159 - 1,159 Effect of foreign currency exchange differences (16,287 ) (2,637,502 ) (8,882,884 ) (251,261 ) (45,291 ) (11,833,225 ) Balance at December 31, 2016 $ 3,365,013 $ 96,258,175 $ 248,200,756 $ 8,474,661 $ 7,713,542 $ 364,012,147 Accumulated depreciation and impairment Balance at January 1, 2016 $ - $ 34,646,878 $ 164,568,298 $ 5,907,414 $ 113,342 $ 205,235,932 Depreciation expenses - 5,114,263 22,983,290 864,061 - 28,961,614 Impairment losses recognized - 620 876,123 5,564 5,924 888,231 Disposals - (449,198 ) (5,544,489 ) (151,875 ) (100,049 ) (6,245,611 ) Reclassification - (5,123 ) 9,660 (4,537 ) - - Acquisitions through business combinations - - - 824 - 824 Effect of foreign currency exchange differences - (1,077,896 ) (7,392,888 ) (236,371 ) (1,929 ) (8,709,084 ) Balance at December 31, 2016 $ - $ 38,229,544 $ 175,499,994 $ 6,385,080 $ 17,288 $ 220,131,906 For the year ended December 31, 2017 Land Buildings and improvements Machinery and equipment Other equipment Construction in progress and machinery in transit Total NT$ NT$ NT$ NT$ NT$ NT$ Cost Balance at January 1, 2017 $ 3,365,013 $ 96,258,175 $ 248,200,756 $ 8,474,661 $ 7,713,542 $ 364,012,147 Additions - 350,434 102,301 130,659 23,094,288 23,677,682 Disposals - (609,294 ) (8,449,949 ) (763,937 ) (73,248 ) (9,896,428 ) Reclassification (35,965 ) 6,483,392 18,331,738 174,947 (25,428,464 ) (474,352 ) Effect of foreign currency exchange differences (70,530 ) (2,294,779 ) (4,986,843 ) (204,250 ) 557,595 (6,998,807 ) Balance at December 31, 2017 $ 3,258,518 $ 100,187,928 $ 253,198,003 $ 7,812,080 $ 5,863,713 $ 370,320,242 Accumulated depreciation and impairment Balance at January 1, 2017 $ - $ 38,229,544 $ 175,499,994 $ 6,385,080 $ 17,288 $ 220,131,906 Depreciation expenses - 5,156,558 22,722,307 746,422 - 28,625,287 Impairment losses recognized - 2,310 286,880 368 - 289,558 Disposals - (478,903 ) (7,540,654 ) (720,319 ) (17,288 ) (8,757,164 ) Reclassification - (210,080 ) 34,452 (24,117 ) - (199,745 ) Effect of foreign currency exchange differences - (784,365 ) (3,990,174 ) (163,467 ) - (4,938,006 ) Balance at December 31, 2017 $ - $ 41,915,064 $ 187,012,805 $ 6,223,967 $ - $ 235,151,836 For the year ended December 31, 2018 Land Buildings and improvements Machinery and equipment Other equipment Construction in progress and machinery in transit Total NT$ NT$ NT$ NT$ NT$ NT$ Cost Balance at January 1, 2018 $ 3,258,518 $ 100,187,928 $ 253,198,003 $ 7,812,080 $ 5,863,713 $ 370,320,242 Additions - 144,898 192,673 84,860 38,669,807 39,092,238 Disposals - (677,206 ) (26,493,282 ) (2,251,060 ) (34,902 ) (29,456,450 ) Reclassification - 5,388,709 32,060,513 2,148,211 (39,612,324 ) (14,891 ) Acquisition through business combinations (Note 30) 6,880,400 37,127,957 95,810,062 11,122,171 5,781,189 156,721,779 Effect of foreign currency exchange differences 27,051 (464,275 ) (929,579 ) (78,095 ) 244,069 (1,200,829 ) Balance at December 31, 2018 $ 10,165,969 $ 141,708,011 $ 353,838,390 $ 18,838,167 $ 10,911,552 $ 535,462,089 Land Buildings and improvements Machinery and equipment Other equipment Construction in progress and machinery in transit Total NT$ NT$ NT$ NT$ NT$ NT$ Accumulated depreciation and impairment Balance at January 1, 2018 $ - $ 41,915,064 $ 187,012,805 $ 6,223,967 $ - $ 235,151,836 Depreciation expenses - 6,325,948 31,751,251 1,816,587 - 39,893,786 Impairment losses recognized - 29,531 97,680 5,860 - 133,071 Disposals - (491,033 ) (25,704,778 ) (2,070,302 ) - (28,266,113 ) Reclassification - (265 ) - - - (265 ) Acquisition through business combinations (Note 30) - 15,097,920 53,210,063 6,428,174 - 74,736,157 Effect of foreign currency exchange differences - (133,091 ) (616,601 ) (29,279 ) - (778,971 ) Balance at December 31, 2018 $ - $ 62,744,074 $ 245,750,420 $ 12,375,007 $ - $ 320,869,501 Land Buildings and improvements Machinery and equipment Other equipment Construction in progress and machinery in transit Total US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) Cost Balance at January 1, 2018 $ 106,453 $ 3,273,046 $ 8,271,741 $ 255,213 $ 191,562 $ 12,098,015 Additions - 4,734 6,294 2,772 1,263,306 1,277,106 Disposals - (22,124 ) (865,511 ) (73,540 ) (1,140 ) (962,315 ) Reclassification - 176,044 1,047,387 70,180 (1,294,097 ) (486 ) Acquisition through business combinations (Note 30) 224,776 1,212,936 3,130,025 363,351 188,866 5,119,954 Effect of foreign currency exchange differences 884 (15,168 ) (30,368 ) (2,551 ) 7,973 (39,230 ) Balance at December 31, 2018 $ 332,113 $ 4,629,468 $ 11,559,568 $ 615,425 $ 356,470 $ 17,493,044 Accumulated depreciation and impairment Balance at January 1, 2018 $ $ 1,369,326 $ 6,109,533 $ 203,331 $ - $ 7,682,190 Depreciation expense - 206,663 1,037,283 59,346 - 1,303,292 Impairment losses recognized - 965 3,191 192 - 4,348 Disposals - (16,042 ) (839,751 ) (67,635 ) - (923,428 ) Reclassification - (9 ) - - - (9 ) Acquisition through business combinations (Note 30) - 493,235 1,738,323 210,003 - 2,441,561 Effect of foreign currency exchange differences - (4,348 ) (20,144 ) (957 ) - (25,449 ) Balance at December 31, 2018 $ - $ 2,049,790 $ 8,028,435 $ 404,280 $ - $ 10,482,505 Due to the Group’s future operation plans and capacity evaluation or production demands in segment of packaging and testing, the Group believed that a portion of property, plant and equipment does not qualify for the production needs and, therefore, recognized an impairment loss of NT$888,231 thousand, NT$289,558 thousand and NT$133,071 thousand (US$4,348 thousand) under the line item of other operating income and expenses in the consolidated statements of comprehensive income (Note 26) for the years ended December 31, 2016, 2017 and 2018, respectively. The recoverable amount of a portion of the impaired property, plant and equipment is determined by its fair value less costs of disposal, of which the fair value is based on the recent quoted prices of assets with similar age and obsolescence that provided by the vendors in secondary market which represent a Level 3 input because the secondary market is not very active. The recoverable amount of the other portion of the impaired property, plant and equipment is determined on the basis of its value in use and the Group expects to derive zero future cash flows from these assets. Each class of property, plant and equipment was depreciated on a straight-line basis over the following useful lives: Buildings and improvements Main plant buildings 10-55 years Cleanrooms 10-20 years Others 3-20 years Machinery and equipment 2-10 years Other equipment 2-20 years The capitalized borrowing costs for the years ended December 31, 2016, 2017 and 2018 are disclosed in Note 26.

Investment Properties

Investment Properties	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Investment Properties	17. INVESTMENT PROPERTIES Land Buildings and improvements Total NT$ NT$ NT$ Cost Balance at January 1, 2017 $ - $ - $ - Additions - 186,535 186,535 Disposals - (342 ) (342 ) Transferred from inventories related to real estate business and property, plant and equipment 35,965 8,114,110 8,150,075 Effects of foreign currency exchange differences - 106,482 106,482 Balance at December 31, 2017 $ 35,965 $ 8,406,785 $ 8,442,750 Accumulated depreciation and impairment Balance at January 1, 2017 $ - $ - $ - Depreciation expenses - 122,231 122,231 Disposals - (161 ) (161 ) Transferred from property, plant and equipment - 199,745 199,745 Effects of foreign currency exchange differences - 1,499 1,499 Balance at December 31, 2017 $ - $ 323,314 $ 323,314 Carrying amount at December 31, 2017 $ 35,965 $ 8,083,471 $ 8,119,436 Land Buildings and improvements Total NT$ NT$ NT$ Cost Balance at January 1, 2018 $ 35,965 $ 8,406,785 $ 8,442,750 Additions - 125,853 125,853 Transferred from property, plant and equipment - 14,891 14,891 Effects of foreign currency exchange differences - (137,739 ) (137,739 ) Balance at December 31, 2018 $ 35,965 $ 8,409,790 $ 8,445,755 Accumulated depreciation and impairment Balance at January 1, 2018 $ - $ 323,314 $ 323,314 Depreciation expenses - 392,667 392,667 Transferred from property, plant and equipment - 265 265 Effects of foreign currency exchange differences - (8,870 ) (8,870 ) Balance at December 31, 2018 $ - $ 707,376 $ 707,376 Carrying amount at December 31, 2018 $ 35,965 $ 7,702,414 $ 7,738,379 Land Buildings and improvements Total US$ (Note 4) US$ (Note 4) US$ (Note 4) Cost Balance at January 1, 2018 $ 1,175 $ 274,642 $ 275,817 Additions - 4,111 4,111 Transferred from property, plant and equipment - 487 487 Effects of foreign currency exchange differences - (4,500 ) (4,500 ) Balance at December 31, 2018 $ 1,175 $ 274,740 $ 275,915 Accumulated depreciation and impairment Balance at January 1, 2018 $ - $ 10,562 $ 10,562 Depreciation expenses - 12,828 12,828 Transferred from property, plant and equipment - 9 9 Effects of foreign currency exchange differences - (290 ) (290 ) Balance at December 31, 2018 $ - $ 23,109 $ 23,109 Carrying amount at December 31, 2018 $ 1,175 $ 251,631 $ 252,806 The investment properties were depreciated on a straight-line basis over the following useful lives: Main buildings 10-40 years Others 3-20 years The fair value of the investment properties was approximately NT$11,560,440 thousand and NT$11,764,829 thousand (US$384,346 thousand) as of December 31, 2017 and 2018, respectively, which was measured using the market approach and the income approach based on level 3 inputs by independent professional appraisers. The significant unobservable inputs were discounted rates. Investment properties are held under freehold interests. Refer to Note 38 for the carrying amount of the investment properties that had been pledged by the Group to secure borrowings.

Goodwill

Goodwill	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Goodwill	18. GOODWILL Cost Accumulated impairment Carrying amount NT$ NT$ NT$ Balance at January 1, 2016 $ 12,495,515 $ 1,988,996 $ 10,506,519 Acquisitions through business combinations (Note 30) 15,323 - 15,323 Effect of foreign currency exchange differences (31,533 ) - (31,533 ) Balance at December 31, 2016 12,479,305 1,988,996 10,490,309 Impairment losses recognized - 425,117 (425,117 ) Effect of foreign currency exchange differences (130,698 ) - (130,698 ) Balance at December 31, 2017 12,348,607 2,414,113 9,934,494 Cost Accumulated impairment Carrying amount NT$ NT$ NT$ Acquisition through business combinations (Note 30) $ 39,990,231 $ - $ 39,990,231 Effect of foreign currency exchange differences 49,721 - 49,721 Balance at December 31, 2018 $ 52,388,559 $ 2,414,113 $ 49,974,446 Cost Accumulated impairment Carrying amount US$ (Note 4) US$ (Note 4) US$ (Note 4) Balance at January 1, 2018 $ 403,418 $ 78,867 $ 324,551 Acquisition through business combinations (Note 30) 1,306,443 - 1,306,443 Effect of foreign currency exchange differences 1,624 - 1,624 Balance at December 31, 2018 $ 1,711,485 $ 78,867 $ 1,632,618 a. Allocating goodwill to cash-generating units Goodwill had been allocated to the following cash-generating units for impairment testing purposes: packaging segment, testing segment, EMS segment and other segment. The carrying amounts of goodwill allocated to cash-generating units were as follows: December 31 2017 2018 Cash-generating units NT$ NT$ US$ (Note 4) Packaging segment $ 1,362,724 $ 35,729,371 $ 1,167,245 Testing segment 7,775,581 13,448,886 439,362 Others 796,189 796,189 26,011 $ 9,934,494 $ 49,974,446 $ 1, 632,618 b. Impairment assessment At the end of each year, the Group performs impairment assessment by reviewing the recoverable amounts based on value in use which incorporates cash flow projections estimated by management covering a five-year period. The cash flows beyond that five-year period have been extrapolated using a steady per annum growth rate. In assessing value in use, the estimated future cash flows are discounted to their present value using annual discount rates which were 9.09%-10.49%, 8.97%-11.29% and 8.01%- 8.57% as of December 31, 2016, 2017 and 2018, respectively. The key assumption used in value in use calculations was the growth rates for operating revenue, which were based on the revenue forecast for the Group and the industry as well as the Group’s historical experience. As of December 31, 2017, the recoverable amount of other segment was lower than its carrying amount since its actual growth in revenue did not meet its forecast previously made by management. The review led to the recognition of an impairment loss of NT$425,117 thousand under the line item of other operating income and expenses, net (Note 26) in the consolidated statements of comprehensive income for the year ended December 31, 2017. Management believed that any reasonably possible change in the key assumptions on which recoverable amount would not cause the aggregate carrying amount of the cash-generating unit to exceed its aggregate recoverable amount significantly.

Other Intangible Assets

Other Intangible Assets	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Other Intangible Assets	19. OTHER INTANGIBLE ASSETS The carrying amounts of each class of other intangible assets were as follows: December 31 2017 2018 NT$ NT$ US$ (Note 4) Customer relationships $ 113,776 $ 10,366,797 $ 338,673 Computer software 864,331 1,159,682 37,886 Patents and acquired specific technology 319,402 19,255,669 629,065 Others 109,356 115,552 3,775 $ 1,406,865 $ 30,897,700 $ 1,009,399 For the year ended December 31, 2016 Customer relationships Computer software Patents and acquired specific technology Others Total NT$ NT$ NT$ NT$ NT$ Cost Balance at January 1, 2016 $ 915,636 $ 3,338,360 $ 154,082 $ 193,338 $ 4,601,416 Additions (Note 37) - 372,188 301,351 1,605 675,144 Disposals or derecognization (41,099 ) (80,537 ) (1,310 ) - (122,946 ) Reclassification - - 786 - 786 Acquisitions through business combinations 41,099 - 64,380 30 105,509 Effect of foreign currency exchange differences - (77,782 ) (4,846 ) (2,581 ) (85,209 ) Balance at December 31, 2016 $ 915,636 $ 3,552,229 $ 514,443 $ 192,392 $ 5,174,700 Accumulated amortization Balance at January 1, 2016 $ 641,234 $ 2,385,038 $ 138,386 $ 54,665 $ 3,219,323 Amortization expense 121,412 345,836 24,154 17,421 508,823 Disposals or derecognization (41,099 ) (58,765 ) (1,310 ) - (101,174 ) Reclassification - - 786 - 786 Acquisitions through business combinations - - 483 23 506 Effect of foreign currency exchange differences - (63,407 ) (7,283 ) (135 ) (70,825 ) Balance at December 31, 2016 $ 721,547 $ 2,608,702 $ 155,216 $ 71,974 $ 3,557,439 For the year ended December 31, 2017 Customer relationships Computer software Patents and acquired specific technology Others Total NT$ NT$ NT$ NT$ NT$ Cost Balance at January 1, 2017 $ 915,636 $ 3,552,229 $ 514,443 $ 192,392 $ 5,174,700 Additions - 265,497 - 12,328 277,825 Disposals - (83,595 ) (123,744 ) (4,978 ) (212,317 ) Effect of foreign currency exchange differences - (47,679 ) (1,213 ) (988 ) (49,880 ) Balance at December 31, 2017 $ 915,636 $ 3,686,452 $ 389,486 $ 198,754 $ 5,190,328 Accumulated amortization Balance at January 1, 2017 $ 721,547 $ 2,608,702 $ 155,216 $ 71,974 $ 3,557,439 Amortization expense 80,313 316,580 43,493 17,280 457,666 Disposals - (72,481 ) (123,743 ) - (196,224 ) Effect of foreign currency exchange differences - (30,680 ) (4,882 ) 144 (35,418 ) Balance at December 31, 2017 $ 801,860 $ 2,822,121 $ 70,084 $ 89,398 $ 3,783,463 For the year ended December 31, 2018 Customer relationships Computer software Patents and acquired specific technology Others Total NT$ NT$ NT$ NT$ NT$ Cost Balance at January 1, 2018 $ 915,636 $ 3,686,452 $ 389,486 $ 198,754 $ 5,190,328 Additions - 528,883 - 8,776 537,659 Disposals - (95,358 ) (231 ) (4,000 ) (99,589 ) Acquisition through business combinations (Note 30) 11,000,000 274,868 20,200,000 32,800 31,507,668 Effect of foreign currency exchange differences - 6,200 (899 ) (332 ) 4,969 Balance at December 31, 2018 $ 11,915,636 $ 4,401,045 $ 20,588,356 $ 235,998 $ 37,141,035 Customer relationships Computer software Patents and acquired specific technology Others Total NT$ NT$ NT$ NT$ NT$ Accumulated amortization Balance at January 1, 2018 $ 801,860 $ 2,822,121 $ 70,084 $ 89,398 $ 3,783,463 Amortization expense 746,979 373,536 1,263,309 18,626 2,402,450 Disposals - (95,202 ) (231 ) (4,000 ) (99,433 ) Acquisition through business combinations (Note 30) - 137,799 - 15,483 153,282 Effect of foreign currency exchange differences - 3,109 (475 ) 939 3,573 Balance at December 31, 2018 $ 1,548,839 $ 3,241,363 $ 1,332,687 $ 120,446 $ 6,243,335 Customer relationships Computer software Patents and acquired specific technology Others Total US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) Cost Balance at January 1, 2018 $ 29,913 $ 120,433 $ 12,724 $ 6,493 $ 169,563 Additions - 17,278 - 287 17,565 Disposals - (3,115 ) (8 ) (131 ) (3,254 ) Acquisition through business combinations 359,359 8,980 659,915 1,072 1,029,326 Effect of foreign currency exchange differences - 202 (29 ) (11 ) 162 Balance at December 31, 2018 $ 389,272 $ 143,778 $ 672,602 $ 7,710 $ 1,213,362 Accumulated amortization Balance at January 1, 2018 $ 26,196 $ 92,196 $ 2,290 $ 2,921 $ 123,603 Amortization expense 24,403 12,203 41,271 608 78,485 Disposals - (3,110 ) (8 ) (131 ) (3,249 ) Acquisition through business combinations - 4,502 - 506 5,008 Effect of foreign currency exchange differences - 101 (16 ) 31 116 Balance at December 31, 2018 $ 50,599 $ 105,892 $ 43,537 $ 3,935 $ 203,963 Each class of other intangible assets was amortized on the straight-line basis over the following useful lives: Customer relationships 11 years Computer software 2-10 years Patents and acquired specific technology 5-15 years Others 5-32 years

Long-term Prepayments for Lease

Long-term Prepayments for Lease	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Long-term Prepayments for Lease	20. LONG-TERM PREPAYMENTS FOR LEASE Long-term prepayments for lease mainly represented land use rights located in China with periods for use from 30 to 70 years and will expire through 2048 to 2089.

Borrowings

Borrowings	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Borrowings	21. BORROWINGS a. Short-term borrowings Bank loans Short-term borrowings mainly represented unsecured revolving bank loans with annual interest rates at 0.80%-4.79% and 0.76%-5.10% as of December 31, 2017 and 2018, respectively. b. Long-term borrowings 1) Bank loans December 31 2017 2018 NT$ NT$ US$ (Note 4) Working capital bank loans Syndicated bank loans - repayable through May 2019 to May 2023, annual interest rates were 2.61% -2.70% and 1.80% as of December 31, 2017 and 2018, respectively $ 4,761,600 $ 55,000,000 $ 1,796,798 Others - repayable through February 2019 to October 2023, annual interest rates were 0.93%-2.10% and 0.75%-3.77% as of December 31, 2017 and 2018, respectively 23,941,947 75,533,354 2,467,604 Mortgage loans Repayable through July 2019 to June 2023, annual interest rates were 4.95%-5.39% and 5.39% as of December 31, 2017 and 2018 4,705,149 4,393,826 143,542 33,408,696 134,927,180 4,407,944 Less: unamortized arrangement fee 1,200 128,083 4,184 33,407,496 134,799,097 4,403,760 Less: current portion 8,261,625 10,779,034 352,141 $ 25,145,871 $ 124,020,063 $ 4,051,619 Pursuant to some of the above working capital bank loans agreements, the Company and its subsidiaries should maintain certain financial covenants including current ratio, leverage ratio, tangible net assets and interest coverage ratio. Such financial ratios are calculated based on each of their annual audited consolidated financial statements or semi-annual reviewed consolidated financial statements. The Company and its subsidiaries were in compliance with all of the financial covenants as of December 31, 2017 and 2018. 2) Long-term bills payable December 31 2017 2018 NT$ NT$ US$ (Note 4) China Bills Finance Corporation, repayable in February 2020, annual interest rate were 0.96% and 0.99% as of December 31, 2017 and 2018, respectively $ 1,000,000 $ 1,000,000 $ 32,669 International Bills Finance Corporation, repayable in March 2020, annual interest rate were 0.96% and %1.00% as of December 31, 2017 and 2018, respectively 1,000,000 1,000,000 32,669 Ta Ching Bills Finance Corporation, repayable in January 2020, annual interest rates was 0.98% as of December 31, 2018 - 1,100,000 35,936 2,000,000 3,100,000 101,274 Less: unamortized discounts 868 768 25 $ 1,999,132 $ 3,099,232 $ 101,249

Bonds Payable

Bonds Payable	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Bonds Payable	22. BONDS PAYABLE December 31 2017 2018 NT$ NT$ US$ (Note 4) Unsecured domestic bonds Repayable at maturity in January 2021 and interest due annually with annual interest rate at 1.30% $ 7,000,000 $ 7,000,000 $ 228,683 Repayable at maturity in January 2023 and interest due annually with annual interest rate at 1.50% 2,000,000 2,000,000 65,338 Repayable at maturity in January 2022 and interest due annually with annual interest rate at 1.25% 3,700,000 3,700,000 120,876 Repayable at maturity in January 2024 and interest due annually with annual interest rate at 1.45% 4,300,000 4,300,000 140,477 December 31 2017 2018 NT$ NT$ US$ (Note 4) Unsecured convertible overseas bonds US$200,000 thousand (linked to New Taiwan dollar) $ 6,185,600 $ - $ - 23,185,600 17,000,000 555,374 Less: discounts on bonds payable 42,820 14,064 459 23,142,780 16,985,936 554,915 Less: current portion 6,161,197 - - $ 16,981,583 $ 16,985,936 $ 554,915 a. In September 2013, ASE offered the third unsecured convertible overseas bonds (the “Bonds”) in US$400,000 thousand. The Bonds are zero coupon bonds with a maturity of 5 years. In 2017, the Bonds holders have exercised the conversion right to convert the Bonds of US$399,600 thousand into ASE’s ordinary shares at conversion prices from NT$27.95 to NT$28.96. Except those have been converted, ASE, based on the board of directors’ resolution, has early redeemed the outstanding Bonds of US$400 thousand in September 2017. b. In July 2015, ASE offered the fourth unsecured convertible overseas bonds (the “Currency Linked Bonds”) in US$200,000 thousand. The Currency Linked Bonds are zero coupon bonds with a maturity of 2.75 years. The Currency Linked Bonds were expired in March 2018 and none has been exercised. ASE redeemed the Currency Linked Bonds in cash in an amount by converting the par value into New Taiwan dollar amount using a fixed exchange rate of US$1 to NT$30.928 and then back to U.S. dollar amount using the applicable prevailing rate at the time of redemption. At the same time, ASE reclassified NT$214,022 thousand from capital surplus arising from equity component of convertible bonds to capital surplus arising from expired share options. c. To focus on corporate sustainability and to carry out the commitment to environmental protection and energy conservation, Anstock II Limited, a subsidiary the Company 100% owned, offered overseas bonds in US$300,000 thousand with the maturity of 3 years and annual interest rate of 2.125% (the “Green Bonds”) in July 2014. The Green Bonds are unconditionally and irrevocably guaranteed by ASE and the proceeds were used to fund certain eligible projects to promote the Group’s transition to low-carbon and climate resilient growth. The Company’s subsidiary has repaid the Green Bonds in July 2017. d. In October 2014, SPIL offered the fourth unsecured convertible overseas bonds (the “SPIL Bonds”) in US$400,000 thousand. The SPIL Bonds are zero coupon bonds with a maturity of 5 years. During May 1, 2018 to June 30, 2018, all outstanding SPIL Bonds of US$148,000 thousand were converted into SPIL’s ordinary shares and then such ordinary shares were repurchased by the Company with a total consideration of NT$5,216,985 thousand (US$170,434 thousand) (NT$51.2 (US$1.67) per ordinary share, 0.3% securities transactions tax not yet deducted) pursuant to the supplemental indenture. In addition, capital surplus arising from the difference between consideration received and the carrying amount of the subsidiaries’ net assets during actual disposal or acquisition was decreased by NT$388,491 thousand (US$12,692 thousand).

Other Payables

Other Payables	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Other Payables	23. OTHER PAYABLES December 31 2017 2018 NT$ NT$ US$ (Note 4) Accrued salary and bonus $ 7,292,254 $ 10,591,202 $ 346,005 Payables for property, plant and equipment 4,623,268 7,995,634 261,210 Accrued employees’ compensation and remuneration to directors 2,568,880 3,038,417 99,262 Accrued employee insurance 657,176 875,638 28,606 Accrued utilities 417,257 427,106 13,953 Payables for patents and acquired specific technology (Note 37) 93,000 57,590 1,882 Others 5,726,052 8,018,295 261,950 $ 21,377,887 $ 31,003,882 $ 1,012,868

Retirement Benefit Plans

Retirement Benefit Plans	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Retirement Benefit Plans	24. RETIREMENT BENEFIT PLANS a. Defined contribution plans 1) The pension plan under the R.O.C. Labor Pension Act (“LPA”) for the Group’s R.O.C. resident employees is a government-managed defined contribution plan. Based on the LPA, the Company and its subsidiaries in Taiwan makes monthly contributions to employees’ individual pension accounts at 6% of their monthly salaries. 2) The subsidiaries located in China, U.S.A., Malaysia, Singapore and Mexico also make contributions at various ranges according to relevant local regulations. b. Defined benefit plans 1) The Company and its subsidiaries in Taiwan joined the defined benefit pension plan under the R.O.C. Labor Standards Law operated by the government. Pension benefits are calculated on the basis of the length of service and average monthly salaries of the last six months before retirement. The Company and its subsidiaries in Taiwan make contributions based on a certain percentage of their domestic employees’ monthly salaries to a pension fund administered by the pension fund monitoring committee. Before the end of each year, the Company and its subsidiaries in Taiwan assess the balance in the pension fund. If the amount of the balance in the pension fund is inadequate to pay retirement benefits for employees who conform to retirement requirements in the next year, the Company and its subsidiaries in Taiwan are required to fund the difference in one appropriation that should be made before the end of March of the next year. Pension contributions are deposited in the Bank of Taiwan in the committee’s name and are managed by the Bureau of Labor Funds, Ministry of Labor (“the Bureau”); the Company and its subsidiaries in Taiwan have no right to influence the investment policy and strategy. 2) ASE Japan has a pension plan under which eligible employees with more than ten years of service are entitled to receive pension benefits based on their length of service and salaries at the time of termination of employment. ASE Japan makes contributions based on a certain amount of pension cost to employees. ASE Korea also has a pension plan under which eligible employees and directors with more than one year of service are entitled to receive a lump-sum payment upon termination of their service with ASE Korea, based on their length of service and salaries at the time of termination. ASE Korea makes contributions based on a certain percentage of pension cost to an external financial institution administered by the management and in the names of employees. 3) ASE, SPIL, ASE Test, Inc. and ASE Electronics Inc. maintain pension plans for executive managers. Pension costs under the plans were NT$6,872 thousand, NT$3,171 thousand and NT$11,137 thousand (US$364 thousand) for the years ended December 31, 2016, 2017 and 2018, respectively. As of December 31, 2017 and 2018, accrued pension liabilities for executive managers were NT$209,637 thousand and NT$320,542 thousand (US$10,472 thousand), respectively. 4) The amounts included in the consolidated balance sheets arising from the Group’s obligation in respect of its defined benefit plans excluding those for executive managers were as follows: December 31 2017 2018 NT$ NT$ US$ (Note 4) Present value of the defined benefit obligation $ 7,910,638 $ 10,297,139 $ 336,398 Fair value of the plan assets (4,341,373 ) (5,492,123 ) (179,423 ) Present value of unfunded defined benefit obligation 3,569,265 4,805,016 156,975 Recorded under other payables (24,638 ) (18,791 ) (614 ) Recorded under other current assets 182,421 11,910 389 Net defined benefit liability $ 3,727,048 $ 4,798,135 $ 156,750 Movements in net defined benefit liability (asset) were as follows: Present Value of the Defined Benefit Obligation Fair Value of the Plan Assets Net Defined Benefit Liability (Asset) NT$ NT$ NT$ Balance at January 1, 2016 $ 7,973,676 $ (3,973,729 ) $ 3,999,947 Service cost Current service cost 329,838 - 329,838 Net interest expense (income) 167,111 (109,080 ) 58,031 Recognized in profit or loss 496,949 (109,080 ) 387,869 Remeasurement Return on plan assets (excluding amounts included in net interest) - 54,549 54,549 Actuarial loss arising from changes in financial assumptions 156,193 - 156,193 Actuarial loss arising from experience adjustments 200,723 - 200,723 Actuarial loss arising from changes in demographic assumptions 5,716 - 5,716 Recognized in other comprehensive income 362,632 54,549 417,181 Contributions from the employer - (807,232 ) (807,232 ) Benefits paid from the pension fund (308,471 ) 308,471 - Benefits paid from the Group (36,033 ) - (36,033 ) Present Value of the Defined Benefit Obligation Fair Value of the Plan Assets Net Defined Benefit Liability (Asset) NT$ NT$ NT$ Liabilities assumed in a business combination $ 535 $ (535 ) $ - Exchange differences on foreign plans (99,404 ) 110,189 10,785 Balance at December 31, 2016 8,389,884 (4,417,367 ) 3,972,517 Service cost Current service cost 278,412 - 278,412 Past service cost and gain on settlements (68,979 ) - (68,979 ) Net interest expense (income) 157,404 (103,741 ) 53,663 Recognized in profit or loss 366,837 (103,741 ) 263,096 Remeasurement Return on plan assets (excluding amounts included in net interest) - 52,124 52,124 Actuarial loss arising from changes in financial assumptions 56,860 - 56,860 Actuarial gain arising from experience adjustments (315,090 ) - (315,090 ) Actuarial loss arising from changes in demographic assumptions 762 - 762 Recognized in other comprehensive income (257,468 ) 52,124 (205,344 ) Contributions from the employer - (484,790 ) (484,790 ) Benefits paid from the pension fund (690,830 ) 690,830 - Benefits paid from the Group (96,575 ) - (96,575 ) Exchange differences on foreign plans 198,790 (78,429 ) 120,361 Balance at December 31, 2017 7,910,638 (4,341,373 ) 3,569,265 Service cost Current service cost 224,126 - 224,126 Net interest expense (income) 178,779 (122,709 ) 56,070 Recognized in profit or loss 402,905 (122,709 ) 280,196 Remeasurement Return on plan assets (excluding amounts included in net interest) - (16,589 ) (16,589 ) Actuarial gain arising from changes in financial assumptions (8,643 ) - (8,643 ) Actuarial loss arising from experience adjustments 302,499 - 302,499 Actuarial loss arising from changes in demographic assumptions 8,190 - 8,190 Actuarial loss arising from changes in other assumptions 22,723 - 22,723 Present Value of the Defined Benefit Obligation Fair Value of the Plan Assets Net Defined Benefit Liability (Asset) NT$ NT$ NT$ Recognized in other comprehensive income $ 324,769 $ (16,589 ) $ 308,180 Contributions from the employer - (364,237 ) (364,237 ) Benefits paid from the pension fund (541,989 ) 541,989 - Benefits paid from the Group (295,953 ) - (295,953 ) Business combinations 2,522,805 (1,210,524 ) 1,312,281 Exchange differences on foreign plans (26,036 ) 21,320 (4,716 ) Balance at December 31, 2018 $ 10,297,139 $ (5,492,123 ) $ 4,805,016 Present Value of the Defined Benefit Obligation Fair Value of the Plan Assets Net Defined Benefit Liability (Asset) US$ (Note 4) US$ (Note 4) US$ (Note 4) Balance at January 1, 2018 $ 258,433 $ (141,829 ) $ 116,604 Service cost Current service cost 7,322 - 7,322 Net interest expense (income) 5,841 (4,009 ) 1,832 Recognized in profit or loss 13,163 (4,009 ) 9,154 Remeasurement Return on plan assets (excluding amounts included in net interest) - (542 ) (542 ) Actuarial gain arising from changes in financial assumptions (282 ) - (282 ) Actuarial loss arising from experience adjustments 9,882 - 9,882 Actuarial loss arising from changes in demographic assumptions 268 - 268 Actuarial loss arising from changes in other assumptions 742 - 742 Recognized in other comprehensive income 10,610 (542 ) 10,068 Contributions from the employer - (11,899 ) (11,899 ) Benefits paid from the pension fund (17,706 ) 17,706 - Benefits paid from the Group (9,669 ) - (9,669 ) Business combinations 82,418 (39,547 ) 42,871 Exchange differences on foreign plans (851 ) 697 (154 ) Balance at December 31, 2018 $ 336,398 $ (179,423 ) $ 156,975 5) The fair value of the plan assets by major categories at each balance sheet date was as follows: December 31 2017 2018 NT$ NT$ US$ (Note 4) Cash $ 2,317,764 $ 2,340,903 $ 76,475 Debt instruments 691,619 902,886 29,497 Equity instruments 1,254,109 2,164,895 70,725 Others 77,881 83,439 2,726 Total $ 4,341,373 $ 5,492,123 $ 179,423 6) Through the defined benefit plans under the Labor Standards Law of the R.O.C., the Group in Taiwan are exposed to the following risks: a) Investment risk The plan assets are invested in equity and debt securities, bank deposits, etc. The investment is conducted at the discretion of the Bureau or under the mandated management. However, in accordance with relevant regulations, the return generated by plan assets should not be below the interest rate for a 2-year time deposit with local banks. b) Interest risk A decrease in the government bond interest rate will increase the present value of the defined benefit obligation; however, this will be partially offset by an increase in the return on the plan’s debt investments. c) Salary risk The present value of the defined benefit obligation is calculated by reference to the future salaries of plan participants. As such, an increase in the salary of the plan participants will increase the present value of the defined benefit obligation. 7) The management of ASE Korea is responsible for the administration of the fund and determination of the investment strategies according to related local regulations. ASE Korea is responsible for the shortfall between the fund and the defined benefit obligation. The plan assets are invested in the certificates of deposits. 8) The present value of the defined benefit obligation and the related current service cost and past service cost were measured using the Projected Unit Credit Method. Except the pension plans for executive managers, the key assumptions used for the actuarial valuations were as follows: December 31 2017 2018 Discount rates (%) 0.06-3.85 0.05-3.02 Expected rates of salary increase (%) 2.00-4.42 1.75-4.06 The sensitivity analysis below has been determined based on reasonably possible changes of the respective assumptions occurring at each balance sheet date, while holding all other assumptions constant. December 31 2017 2018 NT$ NT$ US$ (Note 4) Discount Rate 0.5% higher $ (455,158 ) $ (555,181 ) $ (18,137 ) 0.5% lower $ 461,891 $ 603,089 $ 19,702 Expected rates of salary increase 0.5% higher $ 453,792 $ 591,712 $ 19,331 0.5% lower $ (444,493 ) $ (547,522 ) $ (17,887 ) The sensitivity analysis presented above may not be representative of the actual change in the defined benefit obligation as it is unlikely that the change in assumptions would occur in isolation of one another as some of the assumptions may be correlated. 9) Maturity analysis of undiscounted pension benefit December 31 2017 2018 NT$ NT$ US$ (Note 4) No later than 1 year $ 291,152 $ 368,592 $ 12,042 Later than 1 year but not later than 5 years 1,551,496 1,886,738 61,638 Later than 5 years 16,507,747 13,322,695 435,240 $ 18,350,395 $ 15,578,025 $ 508,920 The Group expected to make contributions of NT$272,911 thousand and NT$484,247 thousand (US$15,820 thousand) to the defined benefit plans in the next year starting from January 1, 2018 and 2019, respectively. As of December 31, 2017 and 2018, the average duration of the defined benefit obligation excluding those for executive managers of the Group was 8 to 14 years and 9 to 15 years, respectively.

Equity

Equity	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Equity	25. EQUITY a. Share capital Ordinary shares December 31 2017 2018 Numbers of shares authorized (in thousands) 10,000,000 5,000,000 Numbers of shares reserved (in thousands) Employee share options 800,000 400,000 Number of shares issued and fully paid (in thousands) 8,738,079 4,321,714 December 31 2017 2018 NT$ NT$ US$ (Note 4) Share capital authorized $ 100,000,000 $ 50,000,000 $ 1,633,453 Share capital reserved Employee share options $ 8,000,000 $ 4,000,000 $ 130,676 Share capital issued and fully paid $ 87,380,787 $ 43,217,144 $ 1,411,864 As disclosed in Note 1, the Company acquired 100% shareholdings of ASE through share exchange at an exchange ratio of 1 ordinary share of ASE for 0.5 ordinary share of the Company. The holders of issued ordinary shares with par value NT$10 per share are entitled the right to vote and receive dividends, except the shares held by the Group’s subsidiaries which are not entitled the right to vote. Before the share exchange, 500,000 thousand ordinary shares included in ASE’s authorized shares as of December 31, 2017 were not yet required to complete the share registration process. In December 2016, ASE’s board of directors approved the issuance of 300,000 thousand ordinary shares for cash capital increase at NT$34.3 per share. ASE has completed the registration formalities for the cash capital increase. As disclosed in Note 22, there were 424,258 thousand ordinary shares issued under the conversion of Bonds in 2017. The record dates of 101,164 thousand and 323,094 thousand ordinary shares were July 13, 2017 and October 13, 2017, respectively. ASE has completed the registration formalities. American Depositary Receipts ASE issued ADSs and each ADS represents 5 ordinary shares of ASE. On April 30, 2018, ASE’s ADSs were fully exchanged to the Company’s ADSs and each of the Company’s ADS represents 2 ordinary shares of the Company. As of December 31, 2017 and 2018, 115,261 thousand and 140,042 thousand ADSs were outstanding and represented approximately 576,305 thousand ordinary shares of ASE and 280,085 thousand ordinary shares of the Company, respectively. b. Capital surplus December 31 2017 2018 NT$ NT$ US$ (Note 4) May be used to offset a deficit, distributed as cash dividends, or transferred to share capital (1) Issuance of ordinary shares $ 21,553,853 $ 12,906,401 $ 421,640 Merger by share exchange - 117,693,658 3,844,942 Conversion of bonds payable 1,930,066 - - Difference between consideration and the carrying amount of the subsidiaries’ net assets during actual disposal or acquisition 7,176,958 6,034,102 197,128 30,660,877 136,634,161 4,463,710 December 31 2017 2018 NT$ NT$ US$ (Note 4) May be used to offset a deficit only Changes in percentage of ownership interest in subsidiaries (2) $ 6,084,895 $ 3,727,336 $ 121,768 Treasury share transactions 1,151,345 182,354 5,957 Exercised employee share options 1,089,178 1,366,480 44,642 Expired share options (Notes 22 and 29) 223,454 645,978 21,103 Share of changes in capital surplus of associates 83,733 87,136 2,847 Dividends that the claim period has elapsed and unclaimed by shareholders - 872 29 8,632,605 6,010,156 196,346 May not be used for any purpose Employee share options 960,888 583,542 19,064 Equity component of convertible bonds 214,022 - - Others (3) 155,936 48,805 1,594 1,330,846 632,347 20,658 $ 40,624,328 $ 143,276,664 $ 4,680,714 1) Such capital surplus may be used to offset a deficit; in addition, when the Company has no deficit, such capital surplus may be distributed as cash dividends or transferred to share capital (limited to a certain percentage of the Company’s capital surplus and once a year). 2) Such capital surplus arises from the effect of changes in ownership interest in a subsidiary resulted from equity transactions other than actual disposal or acquisition, or from changes in capital surplus of subsidiaries accounted for using the equity method. 3) Such capital surplus represents the excess of the carrying amount of related accounts over the par value due to employee share options exercised and the Company has not completed registration formalities. As disclosed in Note 1, share exchange between the Company and ASE was deemed as an organization restructure under common control and the Company recorded the same amounts of equity which were related to ASE’s assets and liabilities (the “continued equity”) and then recognized capital surplus arising from merger by share exchange in the amount of the excess of ASE’s total equity over the Company’s share capital and the continued equity. In addition, the Company’s special shareholders’ meeting held in June 2018 resolved to distribute cash in NT$10,795,980 thousand (US$352,695 thousand) from capital surplus arising from issuance of ordinary shares. c. Retained earnings and dividend policy The Articles of Incorporation of the Company (the “Articles”) provides that annual net income shall be distributed in the following order: 1) Replenishment of deficits; 2) 10.0% as legal reserve; 3) Special reserve appropriated or reversed in accordance with laws or regulations set forth by the authorities concerned; 4) Addition or deduction of realized gains or losses on equity instruments at fair value through other comprehensive income. The Articles also provides the policy of the employees’ compensation and remuneration of directors, refer to employees’ compensation and the remuneration of directors in Note 26(g). The Company is currently in the mature growth stage. To meet the capital needs for business development now and in the future and satisfy the shareholders’ demand for cash inflows, the Company shall use residual dividend policy to distribute dividends, of which the cash dividend is not lower than 30% of the total dividend distribution, with the remainder to be distributed in shares. A distribution plan is also to be made by the board of directors and passed for resolution in the shareholders’ meeting. Appropriation of earnings to legal reserve shall be made until the legal reserve equals the Company’s share capital. Legal reserve may be used to offset deficits. If the Company has no deficit and the legal reserve has exceeded 25% of the Company’s share capital, the excess may be transferred to capital or distributed in cash. Items referred to under Rule No. 1010012865 and Rule No. 1010047490 issued by the FSC and in the directive titled “Questions and Answers for Special Reserves Appropriated Following Adoption of IFRSs” should be appropriated to or reversed from a special reserve by the Company. d. Others equity items 1) Exchange differences on translating foreign operations For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Balance at January 1 $ 4,492,671 $ (1,643,623 ) $ (6,733,659 ) $ (219,982 ) Exchange differences on translating foreign operations (5,843,856 ) (4,952,815 ) 426,186 13,923 Share from associates and joint venture accounted for using the equity method (292,438 ) (137,221 ) 136,608 4,463 Disposal of associates and joint venture accounted for using the equity method - - 282,291 9,222 Balance at December 31 $ (1,643,623 ) $ (6,733,659 ) $ (5,888,574 ) $ (192,374 ) 2) Unrealized gain (loss) on available-for-sale financial assets For the Year Ended December 31, 2016 For the Year Ended December 31, 2017 NT$ NT$ Balance at January 1 $ 588,119 $ (197,314 ) Unrealized gain (loss) arising on revaluation of available-for-sale financial assets (257,240 ) 169,585 Cumulative loss reclassified to profit or loss on impairment of available-for-sale financial assets - 50,206 Cumulative loss (gain) reclassified to profit or loss on disposal of available-for-sale financial assets 7,512 (1,517 ) Share from associates and joint venture accounted for using the equity method (535,705 ) 401,610 Balance at December 31 $ (197,314 ) $ 422,570 3) Unrealized gain (loss) on financial assets at FVTOCI For the Year Ended December 31, 2018 NT$ US$ (Note 4) Balance at January 1 per IAS 39 $ 422,570 $ 13,805 Adjustment on initial application of IFRS 9 (Note 3) (287,053 ) (9,377 ) Balance at January 1 per IFRS 9 135,517 4,428 Unrealized gain (loss) recognized during the year Debt instruments (63,076 ) (2,061 ) Equity instruments (398,513 ) (13,019 ) Share from associates and joint venture accounted for using the equity method (555,271 ) (18,140 ) Realized loss (gain) recognized during the year Disposal of equity instruments and transferred cumulative gain to retained earnings (1,518 ) (50 ) Disposal of associates and joint venture accounted for using the equity method (133,364 ) (4,357 ) Share from associates and joint venture accounted for using the equity method 1,118 36 Balance at December 31 $ (1,015,107 ) $ (33,163 ) e. Treasury shares (in thousand shares) Balance at Balance at January 1 Addition Decrease December 31 2016 Shares held by subsidiaries 145,883 - - 145,883 Shares reserved for bonds conversion 120,000 - - 120,000 265,883 - - 265,883 Balance at Balance at January 1 Addition Decrease December 31 2017 Shares held by subsidiaries 145,883 - - 145,883 Shares reserved for bonds conversion 120,000 - - 120,000 265,883 - - 265,883 2018 Shares held by subsidiaries 145,883 - (72,942 ) 72,941 Shares reserved for bonds conversion 120,000 - (120,000 ) - Shares repurchased from dissenting shareholders in accordance with Business Mergers And Acquisitions Act - 1,852 (1,852 ) - 265,883 1,852 (194,794 ) 72,941 The Company’s shares held by its subsidiaries at each balance sheet date were as follows: Shares Held By Subsidiaries Carrying Amount Carrying Amount Fair Value Fair Value (in thousand NT$ US$ (Note 4) NT$ US$ (Note 4) December 31, 2017 ASE Test 88,200 $ 1,380,721 $ 3,364,848 J&R Holding 46,704 381,709 1,781,749 ASE Test, Inc. 10,979 196,677 418,840 145,883 $ 1,959,107 $ 5,565,437 December 31, 2018 ASE Test 44,100 $ 1,380,721 $ 45,107 $ 2,571,044 $ 83,994 J&R Holding 23,352 381,709 12,470 1,361,415 44,476 ASE Test, Inc. 5,489 196,677 6,425 320,031 10,455 72,941 $ 1,959,107 $ 64,002 $ 4,252,490 $ 138,925 Fair values of the Company’s shares held by subsidiaries are based on the closing price from an available published price quotation, which is a Level 1 input in terms of IFRS 13, at the balance sheet dates. In March 2018, ASE’s board of directors approved, in accordance with Business Mergers and Acquisitions Act, to repurchase ASE’s 1,852 thousand ordinary shares at $38.5 per share held by the shareholders dissenting on the share exchange transaction which has been approved by both of ASE and SPIL’s special shareholders’ meetings on February 12, 2018. In addition, ASE’s board of directors approved a capital reduction in April 2018 to cancel ASE’s 121,852 thousand treasury shares and the record date was April 9, 2018. ASE has completed the registration formalities before April 30, 2018. ASE issued ordinary shares in connection with its merger with its subsidiaries. The shares held by its subsidiaries were reclassified to treasury shares on the proportion owned by ASE. As disclosed in Note 1, ASE’s ordinary shares held by subsidiaries were exchanged to the Company’s ordinary shares on April 30, 2018 in accordance with the joint share exchange agreement. The subsidiaries holding the aforementioned treasury shares retain shareholders’ rights except the rights to participate in any capital increase by cash and voting. f. Non-controlling interests For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Balance at January 1 $ 11,492,545 $ 12,000,551 $ 13,190,129 $ 430,909 Adjustment on initial application of IFRS 15 (Note 3) - - 5,183 169 Balance at January 1 per IFRS 15 11,492,545 12,000,551 13,195,312 431,078 Share of profit for the year 1,253,438 1,677,941 1,204,217 39,341 Other comprehensive income (loss) Exchange difference on translating foreign operations (601,787 ) (334,920 ) (198,365 ) (6,480 ) Unrealized gain on available-for-sale financial assets 1,129 5,763 - - Unrealized loss on equity instruments at FVTOCI - - (23,928 ) (782 ) Remeasurement on defined benefit plans 8,846 (13,724 ) (30,079 ) (983 ) Non-controlling interests arising from acquisition of subsidiaries (Note 30) - - 3,582,866 117,049 Acquisition of non-controlling interests in subsidiaries 42,857 - (2,492,915 ) (81,441 ) Partial disposal of subsidiaries (Note 32) 26,436 (3,055 ) 1,693,064 55,311 Subsidiaries’ buy back of their own outstanding ordinary shares (Note 32) (912,886 ) - (801,884 ) (26,197 ) For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Non-controlling interest relating to outstanding vested employee share options granted by subsidiaries $ 927,823 $ 263,213 $ 1,936,643 $ 63,268 Non-controlling interest relating to outstanding expired employee share options granted by subsidiaries - (159,200 ) - - Cash dividends to non-controlling interests (237,850 ) (246,440 ) (424,815 ) (13,878 ) Balance at December 31 $ 12,000,551 $ 13,190,129 $ 17,639,487 $ 576,265

Profit Before Income Tax

Profit Before Income Tax	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Profit Before Income Tax	26. PROFIT BEFORE INCOME TAX a. Other operating income and expenses, net For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Rental income $ 51,607 $ 131,570 $ 182,411 $ 5,959 Gains (losses) on disposal of property, plant and equipment and other assets (127,159 ) 367,110 (14,644 ) (479 ) Impairment losses on property, plant and equipment and goodwill (888,231 ) (714,675 ) (133,071 ) (4,347 ) Loss on damages and claims (12,778 ) (85,585 ) (24,114 ) (788 ) Others 176,281 410,136 361,001 11,794 $ (800,280 ) $ 108,556 $ 371,583 $ 12,139 b. Other income For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Government subsidy $ 332,758 $ 341,844 $ 435,950 $ 14,242 Interest income 230,067 306,871 466,211 15,231 Dividends income 26,411 59,039 190,397 6,220 $ 589,236 $ 707,754 $ 1,092,558 $ 35,693 c. Other gains, net For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Gain on remeasurement of investments accounted for using the equity method (Note 15) $ - $ - $ 7,421,408 $ 242,451 Net gains on financial assets mandatorily at FVTPL - - 3,388,485 110,699 Gain on disposal of subsidiaries (Note 31) - 5,589,457 - - Net gains (losses) arising on financial instruments held for trading 224,446 (3,111,253 ) (1,398,995 ) (45,704 ) Net gains on financial assets designated as at FVTPL 223,113 327,351 - - Foreign exchange gains (losses), net 1,928,384 3,502,586 (1,015,615 ) (33,180 ) Impairment losses on financial assets (91,886 ) (50,206 ) (521,010 ) (17,021 ) Others (7,513 ) 1,518 - - $ 2,276,544 $ 6,259,453 $ 7,874,273 $ 257,245 d. Finance costs For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Total interest expense for financial liabilities measured at amortized cost $ 2,510,197 $ 2,016,298 $ 3,597,932 $ 117,541 Less: Amounts included in the cost of qualifying assets Inventories related to real estate business (238,469 ) (190,137 ) (11,648 ) (381 ) Property, plant and equipment (54,191 ) (51,262 ) (50,309 ) (1,643 ) Investment properties - (13 ) (89 ) (3 ) 2,217,537 1,774,886 3,535,886 115,514 Other finance costs 43,538 24,608 32,355 1,057 $ 2,261,075 $ 1,799,494 $ 3,568,241 $ 116,571 Information relating to the capitalized borrowing costs was as follows: For the Year Ended December 31 2016 2017 2018 Annual interest capitalization rates Inventories related to real estate business (%) 4.35-6.00 4.35-5.39 4.35 Property, plant and equipment (%) 1.15-4.42 1.26-5.49 1.84-4.52 Investment properties (%) - 1.26-1.97 1.84-2.23 e. Depreciation and amortization For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Property, plant and equipment $ 28,961,614 $ 28,625,287 $ 39,893,786 $ 1,303,293 Investment properties - 122,231 392,667 12,828 Intangible assets 508,823 457,666 2,402,450 78,486 Total $ 29,470,437 $ 29,205,184 $ 42,688,903 $ 1,394,607 Summary of depreciation by function Operating costs $ 26,948,106 $ 26,731,714 $ 37,903,050 $ 1,238,257 Operating expenses 2,013,508 2,015,804 2,383,403 77,864 $ 28,961,614 $ 28,747,518 $ 40,286,453 $ 1,316,121 Summary of amortization by function Operating costs $ 152,987 $ 140,175 $ 1,394,664 $ 45,562 Operating expenses 355,836 317,491 1,007,786 32,924 $ 508,823 $ 457,666 $ 2,402,450 $ 78,486 f. Operating expenses directly related to investment properties For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Direct operating expenses of investment properties that generated rental income $ - $ 465,458 $ 1,276,751 $ 41,710 g. Employee benefits expense For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Post-employment benefits Defined contribution plans $ 2,356,416 $ 2,340,826 $ 2,965,054 $ 96,865 Defined benefit plans 394,741 266,267 291,333 9,518 2,751,157 2,607,093 3,256,387 106,383 Equity-settled share-based payments 470,788 438,765 215,648 7,045 Other employee benefits 49,525,940 51,043,198 63,940,430 2,088,874 $ 52,747,885 $ 54,089,056 $ 67,412,465 $ 2,202,302 Summary of employee benefits expense by function Operating costs $ 35,588,529 $ 35,978,403 $ 45,363,170 $ 1,481,972 Operating expenses 17,159,356 18,110,653 22,049,295 720,330 $ 52,747,885 $ 54,089,056 $ 67,412,465 $ 2,202,302 h. Employees’ compensation and the remuneration to directors The Articles stipulates to distribute employees’ compensation and remuneration of directors at the rates in 0.01%-1.00% and no higher than 0.75%, respectively, of net profit before income tax, employees’ compensation and remuneration of directors. For the period from April 30, 2018 to December 31, 2018, the employees’ compensation and the remuneration of directors were NT$45,430 thousand (US$1,484 thousand) and NT$34,073 thousand (US$1,113 thousand) which were accrued based on 0.20% and 0.15%, respectively, of net profit before income tax, employees’ compensation and remuneration to directors. If there is a change in the proposed amounts after the consolidated financial statement authorized for issue, the differences are recorded as a change in accounting estimate and will be adjusted in the following year.

Income Tax

Income Tax	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Income Tax	27. INCOME TAX a. Income tax recognized in profit or loss The major components of income tax were as follows: For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Current income tax In respect of the current year $ 4,177,900 $ 4,979,766 $ 5,207,309 $ 170,118 Income tax on unappropriated earnings 829,345 1,076,353 (1,022,560 ) (33,406 ) Changes in estimate for prior years 28,160 (88,162 ) (103,822 ) (3,392 ) 5,035,405 5,967,957 4,080,927 133,320 Deferred income tax In respect of the current year 574,541 534,472 (227,327 ) (7,426 ) Effect of tax rate changes 14,184 - 657,346 21,475 Changes in estimate for prior years (206,788 ) 52,872 5,696 186 Effect of foreign currency exchange differences (26,498 ) (31,698 ) (3,273 ) (107 ) 355,439 555,646 432,442 14,128 Income tax expense recognized in profit or loss $ 5,390,844 $ 6,523,603 $ 4,513,369 $ 147,448 A reconciliation of income tax expense calculated at the statutory rates and income tax expense recognized in profit or loss was as follows: For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Profit before income tax $ 27,968,705 $ 31,020,663 $ 31,937,678 $ 1,043,374 Income tax expense calculated at the statutory rates $ 8,634,187 $ 10,890,498 $ 13,540,599 $ 442,359 Nontaxable expense (income) in determining taxable income (34,954 ) 483,715 353,019 11,533 Tax-exempt income (700,274 ) (623,566 ) (2,515,453 ) (82,177 ) Additional income tax on unappropriated earnings 829,345 1,076,353 (1,022,560 ) (33,406 ) For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Loss carry-forward and income tax credits currently used $ (898,700 ) $ (1,124,043 ) $ (971,124 ) $ (31,726 ) Remeasurement of deferred income tax assets, net (2,797,673 ) (4,131,473 ) (4,776,271 ) (156,036 ) Changes in estimate for prior periods 28,160 (88,162 ) (103,822 ) (3,392 ) Withholding tax 81,543 40,281 8,981 293 Land value increment tax 249,210 - - - Income tax expense recognized in profit or loss $ 5,390,844 $ 6,523,603 $ 4,513,369 $ 147,448 For the years ended December 31, 2016 and 2017, the Group applied a tax rate of 17% for resident entities subject to the Income Tax Law of the R.O.C. In February 2018, the Income Tax Law of the R.O.C. was amended and the corporate income tax rate was adjusted from 17% to 20% effective in 2018. In addition, the rate of the corporate surtax applicable to 2018 unappropriated earnings is reduced from 10% to 5%. The subsidiaries located in China applied tax rate of 25%. For other jurisdictions, the Group measures taxes by using the applicable tax rate for each individual jurisdiction. b. Income tax recognized directly in equity For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Deferred income tax Related to employee share options $ (204 ) $ 262 $ (1,099 ) $ (36 ) c. Income tax recognized in other comprehensive income For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Deferred income tax Related to remeasurement of defined benefit plans $ 73,637 $ (51,217 ) $ 55,346 $ 1,808 Effect of tax rate changes - - 70,755 2,312 Income tax recognized in other comprehensive income $ 73,637 $ (51,217 ) $ 126,101 $ 4,120 d. Current tax assets and liabilities December 31 2017 2018 NT$ NT$ US$ (Note 4) Current tax assets Tax refund receivable $ 28,458 $ 50,456 $ 1,648 Prepaid income tax 232,084 473,807 15,479 $ 260,542 $ 524,263 $ 17,127 Current tax liabilities Income tax payable $ 7,619,328 $ 6,781,136 $ 221,553 e. Deferred tax assets and liabilities The Group offset certain deferred tax assets and deferred tax liabilities which met the offset criteria. The movements of deferred tax assets and deferred tax liabilities were as follows: For the year ended December 31, 2016 Balance at January 1 Recognized in Profit or Loss Recognized in Other Comprehensive Income Recognized in Equity Exchange Differences Acquisitions Through Business Combinations Balance at December 31 NT$ NT$ NT$ NT$ NT$ NT$ NT$ Deferred tax assets (liabilities) Temporary differences Property, plant and equipment $ (3,504,458 ) $ (182,291 ) $ - $ - $ (72,098 ) $ - $ (3,758,847 ) Defined benefit obligation 845,939 (48,601 ) 73,637 - 2,509 - 873,484 FVTPL financial instruments (232,198 ) 212,737 - - (1,902 ) - (21,363 ) Others 1,384,987 (283,179 ) - (204 ) (21,780 ) - 1,079,824 (1,505,730 ) (301,334 ) 73,637 (204 ) (93,271 ) - (1,826,902 ) Loss carry-forward 1,323,577 (110,967 ) - - (91,008 ) 2,939 1,124,541 Investment credits 351,119 56,862 - - (25,245 ) - 382,736 $ 168,966 $ (355,439 ) $ 73,637 $ (204 ) $ (209,524 ) $ 2,939 $ (319,625 ) For the year ended December 31, 2017 Balance at January 1 Recognized in Profit or Loss Recognized in Other Comprehensive Income Recognized in Equity Exchange Differences Acquisitions Through Business Combinations Balance at December 31 NT$ NT$ NT$ NT$ NT$ NT$ NT$ Deferred tax assets (liabilities) Temporary differences Property, plant and equipment $ (3,758,847 ) $ (101,576 ) $ - $ - $ (18,643 ) $ - $ (3,879,066 ) Defined benefit obligation 873,484 (26,736 ) (51,217 ) - (15,291 ) - 780,240 FVTPL financial instruments (21,363 ) (86,342 ) - - 2,802 - (104,903 ) Others 1,079,824 (22,748 ) - 262 (28,929 ) - 1,028,409 (1,826,902 ) (237,402 ) (51,217 ) 262 (60,061 ) - (2,175,320 ) Loss carry-forward 1,124,541 (456,246 ) - - 13,146 - 681,441 Investment credits 382,736 138,002 - - 13,475 - 534,213 $ (319,625 ) $ (555,646 ) $ (51,217 ) $ 262 $ (33,440 ) $ - $ (959,666 ) For the year ended December 31, 2018 Balance at January 1 Adjustment on initial Application of IFRS 15 Recognized in Profit or Loss Recognized in Other Comprehensive Income Recognized in Equity Exchange Differences Acquisitions Through Business Combinations Balance at December 31 NT$ NT$ NT$ NT$ NT$ NT$ NT$ NT$ Deferred tax assets (liabilities) Temporary differences Property, plant and equipment $ (3,879,066 ) $ - $ (600,229 ) $ - $ - $ (21,146 ) $ (45,873 ) $ (4,546,314 ) Defined benefit obligation 780,240 - (131,687 ) 126,101 - 27,884 262,286 1,064,824 FVTPL financial instruments (104,903 ) - 284,659 - - (137 ) 27,402 207,021 Others 1,028,409 (97,358 ) (26,147 ) - (1,099 ) 74,327 294,540 1,272,672 (2,175,320 ) (97,358 ) (473,404 ) 126,101 (1,099 ) 80,928 538,355 (2,001,797 ) Loss carry-forward 681,441 - (50,059 ) - - 28,293 12,600 672,275 Investment credits 534,213 - 91,021 - - 5,932 - 631,166 $ (959,666 ) $ (97,358 ) $ (432,442 ) $ 126,101 $ (1,099 ) $ 115,153 $ 550,955 $ (698,356 ) Balance at January 1 Adjustment on initial Application of IFRS 15 Recognized in Profit or Loss Recognized in Other Comprehensive Income Recognized in Equity Exchange Differences Acquisitions Through Business Combinations Balance at December 31 US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) Deferred tax assets (liabilities) Temporary differences Property, plant and equipment $ (126,726 ) $ - $ (19,609 ) $ - $ - $ (691 ) $ (1,499 ) $ (148,525 ) Defined benefit obligation 25,490 - (4,302 ) 4,120 - 911 8,569 34,788 FVTPL financial instruments (3,427 ) - 9,300 - - (4 ) 895 6,764 Others 33,597 (3,181 ) (854 ) - (36 ) 2,428 9,622 41,576 (71,066 ) (3,181 ) (15,465 ) 4,120 (36 ) 2,644 17,587 (65,397 ) Loss carry-forward 22,262 - (1,635 ) - - 924 412 21,963 Investment credits 17,452 - 2,973 - - 194 - 20,619 $ (31,352 ) $ (3,181 ) $ (14,127 ) $ 4,120 $ (36 ) $ 3,762 $ 17,999 $ (22,815 ) f. Items for which no deferred tax assets have been recognized for loss carry-forward, investment credits and deductible temporary differences December 31 2017 2018 NT$ NT$ US$ (Note 4) Loss carry-forward $ 542,054 $ 666,043 $ 21,759 Deductible temporary differences 712,141 332,255 10,854 $ 1,254,195 $ 998,298 $ 32,613 The unrecognized loss carry-forward will expire through 2030. g. Information about unused loss carry-forward, unused investment credits, tax-exemption and other tax relief As of December 31, 2018, the unused loss carry-forward comprised of: Expiry Year NT$ US$ (Note 4) 2019 $ 163,916 $ 5,355 2020 290,460 9,489 Expiry Year NT$ US$ (Note 4) 2021 $ 159,641 $ 5,215 2022 94,287 3,080 2023 and thereafter 630,015 20,582 $ 1,338,319 $ 43,721 As of December 31, 2018, unused investment credits comprised of: Remaining Creditable Amount Tax Credit Source NT$ US$ Expiry Year (Note 4) Purchase of machinery and equipment $ 590,694 $ 19,297 2022 Others 40,472 1,322 2023 and thereafter $ 631,166 $ 20,619 As of December 31, 2018, profits attributable to the following expansion projects were exempted from income tax for a 5-year period: Tax-exemption Period Construction and expansion of 2007 by ASE 2016.01-2020.12 Construction and expansion of 2008 by ASE 2014.01-2018.12 Construction and expansion of 2008 by ASE Test Inc. 2014.01-2018.12 Construction and expansion of 2009 by ASE Test Inc. 2018.01-2022.12 Construction and expansion of 2008 by ASE Electronics Inc. 2016.01-2020.12 Construction and expansion of 2007 by SPIL 2015.01-2019.12 Some China subsidiaries qualified as high technology enterprises were entitled to a reduced income tax rate of 15% and were eligible to deduct certain times of research and development expenses from their taxable income. h. Unrecognized deferred tax liabilities associated with investments As of December 31, 2017 and 2018, the taxable temporary differences associated with the investments in subsidiaries for which no deferred tax liabilities have been recognized were NT$16,401,422 thousand and NT$28,810,874 thousand (US$941,224 thousand), respectively. i. Income tax assessments The tax returns of the Company’s R.O.C. subsidiaries through 2014 to 2016 have been examined by the tax authorities.

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Earnings Per Share	28. EARNINGS PER SHARE The earnings and weighted average number of ordinary shares outstanding in the computation of earnings per share were as follows: Net profit for the year For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Profit for the year attributable to owners of the Company $ 21,324,423 $ 22,819,119 $ 26,220,721 $ 856,606 Effect of potentially dilutive ordinary shares: From subsidiaries (374,359 ) (813,627 ) (418,295 ) (13,665 ) From the investments in associates (494,388 ) (367,687 ) - - From convertible bonds (1,165,506 ) 93,781 - - Earnings used in the computation of diluted earnings per share $ 19,290,170 $ 21,731,586 $ 25,802,426 $ 842,941 Weighted average number of ordinary shares outstanding For the Year Ended December 31 2016 2017 Before After Before After Retrospectively Retrospectively Retrospectively Retrospectively Adjusted Adjusted Adjusted Adjusted 2018 Weighted average number of ordinary shares in the computation of basic earnings per share 7,662,870 3,831,435 8,160,887 4,080,443 4,245,247 Effect of potentially dilutive ordinary shares: From convertible bonds 515,295 257,648 124,911 62,456 - From employee share options 59,218 29,609 39,868 19,934 5,103 From employees’ compensation 46,746 23,373 43,574 21,787 779 Weighted average number of ordinary shares in computation of diluted earnings per share 8,284,129 4,142,065 8,369,240 4,184,620 4,251,129 For purposes of the ADS calculation, the denominator represents the aforementioned weighted average outstanding shares divided by 5 (one ADS represents 5 ordinary shares) for each of the two years in the period ended December 31, 2017 before retrospectively adjusted and by 2 (one ADS represents 2 ordinary shares) for each of the two years in the period ended December 31, 2017 after retrospectively adjusted and the year ended December 31, 2018, respectively. The numerator was the same. The share exchange between the Company and ASE was deemed as an organization restructure under common control, and the earnings per share of prior periods were calculated based on weighted average number of ordinary shares outstanding retrospectively adjusted in accordance with share exchange ratio stated in the joint share exchange agreement. The share exchange between the Company and ASE was deemed as an organization restructure under common control, and the earnings per share of prior periods were calculated based on weighted average number of ordinary shares outstanding retrospectively adjusted in accordance with share exchange ratio stated in the joint share exchange agreement. The Group is able to settle the employees’ compensation by cash or shares. The Group assumed that the entire amount of the compensation would be settled in shares and the resulting potential shares were included in the weighted average number of ordinary shares outstanding used in the computation of diluted earnings per share if the effect is dilutive. Such dilutive effect of the potential shares was included in the computation of diluted earnings per share until the shareholders approve the number of shares to be distributed to employees at their meeting in following year. The third unsecured convertible overseas bonds issued by ASE were anti-dilutive for the year ended December 31, 2017 and were excluded from the computation of diluted earnings per share for the respective year.

Share-based Payment Arrangement

Share-based Payment Arrangements	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Share-based Payment Arrangements	29. SHARE-BASED PAYMENT ARRANGEMENTS a. Employee share option plans of the Company The Company’s Option Plan In order to attract, retain and reward employees, the Company has its employee share option plan for full-time employees of the Group and registered 150,000 thousand share options in 2018. Each share option represents the right to purchase one ordinary share of the Company when exercised. Under the terms of the plan, share options are granted at an exercise price equal to or not less than the closing price of the ordinary shares listed on the Taiwan Stock Exchange (the “TSE”) at the issue date. The right of those share options granted under the plan is valid for 10 years, non-transferable and exercisable at certain percentages subsequent to the second anniversary of the grant date. For any subsequent changes in the Company’s capital structure or when cash dividend per ordinary share exceeds 1.5% of the market price per ordinary share, the exercise price is accordingly adjusted. ASE’s Option Plans ASE had five employee share option plans for the Group’s full-time employees. Each share option represents the right to purchase one ordinary share of ASE when exercised. Under the terms of the plans, share options are granted at an exercise price equal to or not less than the closing price of the ordinary shares listed on the TSE at the issue date. The option rights of these plans are valid for 10 years, non-transferable and exercisable at certain percentages subsequent to the second anniversary of the grant date. For any subsequent changes in ASE’s capital structure, the exercise price was accordingly adjusted. As disclosed in Note 1, the Company assumed ASE’s obligations of outstanding employee share option plans starting from April 30, 2018 and each share option represents the right to purchase 0.5 ordinary share of the Company with all other terms and conditions held constant. Information about share options for the years ended December 31, 2016 and 2017 and for the period from January 1, 2018 to April 29, 2018 was as follows: For the Year Ended December 31 For the Period from January 1, 2018 2016 2017 to April 29, 2018 Weighted Weighted Weighted Average Average Average Number of Exercise Number of Exercise Number of Exercise Options Price Options Price Options Price (In Per Share (In Per Share (In Per Share Thousands) (NT$) Thousands) (NT$) Thousands) (NT$) Balance, beginning of period 252,607 $ 26.6 210,795 $ 27.3 135,961 $ 30.2 Options forfeited (6,056 ) 34.6 (5,407 ) 36.3 (1,692 ) 36.3 Options expired - - (1,790 ) 21.1 - - Options exercised (35,756 ) 20.9 (67,637 ) 21.0 (20,557 ) 26.0 Options transferred to the Company in accordance with the joint share exchange agreement - - - - (113,712 ) 30.9 Balance, end of period 210,795 27.3 135,961 30.2 - - Options exercisable, end of period 123,007 20.8 85,642 26.5 - - Starting from April 30, 2018, information about the share option plans that the Company granted and assumed was as follows: For the Period from April 30, 2018 to December 31, 2018 Weighted Average Number of Exercise Price Options Per Share (In Thousands) (NT$) Balance, beginning of period - $ - Transferred from ASE 56,856 61.7 Options granted 131,863 56.4 Options forfeited (1,582 ) 71.5 Options exercised (3,323 ) 43.6 Balance, end of period 183,814 58.1 Options exercisable, end of period 36,354 58.1 Fair value of options granted (NT$) $ 16.28-19.12 The weighted average share price at exercise dates of share options for each of the two years in the period ended December 31, 2017, the period from January 1, 2018 to April 29, 2018 and the period from April 30, 2018 to December 31, 2018 was NT$36.2, NT$37.6, NT$41.0 (US$1.3) and NT$68.5 (US$2.2), respectively. The options granted in 2007 were expired in December 2017 and, therefore, NT$47,087 thousand was reclassified from capital surplus arising from employee share options to capital surplus arising from expired share options. Information about the outstanding share options that the Company granted and assumed at each balance sheet date was as follows: Range of Exercise Price Per Share (NT$) Weighted Average Remaining Contractual Life (Years) December 31, 2017 ASE 4 th $ 20.4-22.6 2.5 ASE 5 th 36.5 7.7 December 31, 2018 ASE 4 th 40.8-45.2 1.5 ASE 5 th 73.0 6.7 The Company 1 st 56.4 9.9 b. Employee share option plans of subsidiaries ASE Mauritius Inc.’s Option Plan ASE Mauritius Inc. has an employee share option plan for full-time employees of the Group which granted 30,000 thousand units in December 2007. Under the terms of the plan, each unit represents the right to purchase one ordinary share of ASE Mauritius Inc. when exercised. The option rights of the plan are valid for 10 years, non-transferable and exercisable at certain percentages subsequent to the second anniversary of the grant date. The option rights of the plan was expired in December 2017, of which shares had not been exercised and, therefore, NT$159,200 thousand was reclassified from non-controlling interest to capital surplus arising from expired employee share options. Information about share options was as follows: For the Year Ended December 31 2016 2017 Number of Exercise Number of Exercise Options Price Options Price (In Per Share (In Per Share Thousands) (US$) Thousands) (US$) Balance at January 1 28,470 $ 1.7 28,470 $ 1.7 Options forfeited - - (250 ) 1.7 Options expired - - (28,220 ) 1.7 Balance at December 31 28,470 1.7 - - Options exercisable, end of year 28,470 1.7 - - USIE’s Option Plan The terms of the plans issued by USIE were the same with those option plans previously granted by ASE. Information about share options was as follows: For the Year Ended December 31 2016 2017 2018 Number of Weighted Exercise Number of Weighted Exercise Number of Weighted Exercise Options Price Options Price Options Price (In Per Share (In Per Share (In Per Share Thousands) (US$) Thousands) (US$) Thousands) (US$) Balance at January 1 29,695 $ 2.1 25,933 $ 2.2 25,556 $ 2.2 Options exercised (3,762 ) 2.0 (377 ) 1.9 (8,845 ) 2.2 Balance at December 31 25,933 2.2 25,556 2.2 16,711 2.1 Options exercisable, end of year 25,933 2.2 25,556 2.2 16,711 2.1 Information about USIE’s outstanding share options at each balance sheet date was as follows: Range of Exercise Price Per Share (US$) Weighted Average Remaining Contractual Life (Years) December 31, 2017 1 st $ 1.5 3.0 2 nd rd 2.4-2.9 2.9 December 31, 2018 1 st 1.5 2.0 2 nd rd 2.4-2.9 2.1 In 2017 and 2018, the Group’s shareholdings of USIE decreased because USIE’s share options had been exercised. The transaction was accounted for as an equity transaction since the Group did not cease to have control over USIE and, as a result, capital surplus was decreased by NT$52,388 thousand and NT$1,239,456 thousand (US$40,492 thousand) in 2017 and 2018, respectively. USISH’s Option Plans Each unit represents the right to purchase one ordinary share of USISH when exercised. The options are valid for 10 years, non-transferable and exercisable at certain percentages subsequent to the second anniversary of the grant date incorporated with certain performance conditions. For any subsequent changes in USISH’s capital structure, the exercise price is accordingly adjusted. Information about share options was as follows: For the Year Ended December 31 2016 2017 2018 Number of Exercise Number of Exercise Number of Exercise Options Price Options Price Options Price (In Per Share (In Per Share (In Per Share Thousands) (CNY) Thousands) (CNY) Thousands) (CNY) Balance at January 1 26,627 $ 15.5 24,997 $ 15.5 22,341 $ 15.5 Options forfeited (1,630 ) 15.5 (2,656 ) 15.5 (804 ) 15.5 Balance at December 31 24,997 15.5 22,341 15.5 21,537 15.5 Options exercisable, end of year - - 8,896 15.5 12,884 15.5 As of December 31, 2017 and 2018, the remaining contractual life of the share options were 7.9 years and 6.9 years, respectively. For the years ended December 31, 2016, 2017 and 2018, employee benefits expense recognized on the aforementioned employee share option plans were NT$470,788 thousand, NT$354,765 thousand and NT$215,648 thousand (US$7,045 thousand), respectively. c. New shares reserved for subscription by employees under cash capital increase As disclosed in Note 25, the board of directors of ASE approved the cash capital increase in December 2016 and, as required under the Company Act in the R.O.C., simultaneously granted options to employees to purchase 10% of such newly issued shares. The grant of the options was accounted for as employee options, accordingly a share-based compensation, and was measured at fair value in accordance with IFRS 2. ASE recognized employee benefits expense and capital surplus arising from exercised employee share options of NT$84,000 thousand in full at the grant date (also the vested date), of which 4,836 thousand shares has not been exercised and, therefore, NT$13,541 thousand was reclassified from capital surplus arising from exercised employee share options to capital surplus arising from expired share options. Information about ASE’s employee share options related to the aforementioned newly issued shares was as follows: Number of Options (In Thousand) Options granted for the year ended 2017 30,000 Options exercised for the year ended 2017 25,164 Fair value of options granted (NT$ per share) $ 2.80 Fair value was measured using the Black-Scholes Option Pricing Model and the inputs to the model were as follows: Share price at the grant date NT$36.55 per share Exercise price NT$34.30 per share Expected volatility 27.15% Expected lives 47 days Expected dividend yield - Risk free interest rate 0.37% Expected volatility was based on ASE’s historical share prices volatility. d. Fair value of share options granted by the Company in 2018 were measured at the grant date by using the trinomial tree model, and the inputs to the model were as follows: Share price at the grant date NT$58.80 per share Exercise price NT$56.40 per share Expected volatility 27.77%-28.86% Expected lives 4.8 years-7.0 years Expected dividend yield - Risk free interest rate 0.73%-0.80% Expected volatility was based on the Company’s and ASE’s historical share prices volatility.

Business Combinations

Business Combinations	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Business Combinations	30. BUSINESS COMBINATIONS Acquisition of TLJ a. Subsidiary acquired Principal Activity Date of Acquisition Proportion of Voting Equity Interests Acquired Cash Consideration NT$ TLJ Engaged in information software services May 3, 2016 60 % $ 89,998 In May 2016, the ASE’s subsidiary, ASE Test, Inc., acquired 60% shareholdings of TLJ with a total consideration determined primarily based on independent professional appraisal reports. NT$41,739 thousand out of the total consideration was paid to key management personnel and related parties. b. Assets acquired and liabilities assumed at the date of acquisition NT$ Current assets $ 16,645 Non-current assets 108,486 Current liabilities (7,599 ) Fair value of identifiable net assets acquired $ 117,532 c. Goodwill recognized on acquisition NT$ Consideration transferred (paid in cash) $ 89,998 Add: Non-controlling interests 42,857 Less: Fair value of identifiable net assets acquired (117,532 ) Goodwill recognized on acquisition $ 15,323 The non-controlling interest recognized at the acquisition date was measured at its fair value. The goodwill recognized mainly represents the control premium. In addition, the consideration paid for the acquisition effectively included amounts attributed to the benefits of expected revenue growth and future market development of TLJ. These benefits are not recognized separately from goodwill because they do not meet the recognition criteria for identifiable intangible assets. The goodwill recognized on acquisition is not expected to be deductible for tax purpose. d. Net cash outflow on acquisition of subsidiaries NT$ Consideration paid in cash $ 89,998 Less: Cash acquired (16,561 ) $ 73,437 Acquisition of SPIL a. Subsidiaries acquired Subsidiary Principal Activity Date of Acquisition Proportion of Voting Equity Interests Acquired (%) Consideration Transferred NT$ US$ (Note 4) SPIL Engaged in the assembly, testing and turnkey services of integrated circuits. April 30, 2018 100 % $ 168,440,585 $ 5,502,796 As disclosed in Note 1, the Company acquired 100% shareholdings of SPIL at NT$51.2 (US$1.7) in cash per SPIL’s ordinary share in accordance with the joint share exchange agreements between ASE and SPIL. b. Assets acquired and liabilities assumed at the date of acquisition NT$ US$ (Note 4) Assets Cash and cash equivalents $ 20,088,970 $ 656,288 Trade and other receivables 15,840,649 517,499 Inventories 5,693,644 186,006 NT$ US$ (Note 4) Property, plant and equipment $ 81,985,622 $ 2,678,393 Intangible assets 31,354,386 1,024,318 Others 24,945,922 814,960 Liabilities Trade and other payables (19,755,598 ) (645,396 ) Borrowings and bonds payables (24,157,174 ) (789,192 ) Others (3,963,201 ) (129,474 ) Fair value of identifiable net assets acquired $ 132,033,220 $ 4,313,402 c. Goodwill recognized on acquisitions NT$ US$ (Note 4) Total consideration $ 168,440,585 $ 5,502,796 Add: Non-controlling interests 3,582,866 117,049 Less: Fair value of identifiable net assets acquired (132,033,220 ) (4,313,402 ) Goodwill recognized on acquisition $ 39,990,231 $ 1,306,443 The fair value of non-controlling interests were determined using market approach based on the valuation multiples of The goodwill recognized in the acquisition of SPIL mainly represents the control premium included in the cost of the combination. In addition, the consideration paid for the combination effectively included amounts attributed to the benefits of expected synergies, revenue growth and future market development of SPIL. These benefits are not recognized separately from goodwill because they do not meet the recognition criteria for identifiable intangible assets. The goodwill recognized on acquisition is not expected to be deductible for tax purpose. d. Net cash outflow on acquisition of subsidiaries NT$ US$ (Note 4) Total consideration $ 168,440,585 $ 5,502,796 Less: Payable for consideration representing the ordinary shares originally held by ASE (53,109,760 ) (1,735,046 ) Less: Cash and cash equivalent acquired (20,088,970 ) (656,288 ) $ 95,241,855 $ 3,111,462 e. Impact of acquisitions on the results of the Group As of December 31, 2018, the results of operations from SPIL since the acquisition date were included in the consolidated statements of comprehensive income and were as follows: NT$ US$ (Note 4) Operating revenue $ 61,247,727 $ 2,000,906 Profit $ 7,627,382 $ 249,179 Had these business combinations been in effect at the beginning of the annual reporting period and the investments in SPIL originally accounted for using the equity method, as disclosed in Note 15, been remeasured to their fair value on January 1, 2018, the Group’s operating revenue for the year ended December 31, 2018 would have been NT$397,261,461 thousand (US$12,978,159 thousand), and profit for the year ended December 31, 2018 would have been NT$25,674,641 thousand (US$838,766 thousand), respectively. This pro forma information is for illustrative purposes only and is not necessarily an indication of the operating revenue and results of operations of the Group that actually would have been achieved had the acquisition been completed on January 1, 2018, nor is it intended to be a projection of future results. In determining the pro forma operating revenue and profit of the Company had SPIL been acquired at the beginning of the current reporting period, the management: 1) Calculated the depreciation of property, plant and equipment and the amortization of intangible assets acquired on the basis of the fair values at the initial accounting for the business combination rather than the carrying amounts recognized in the respective pre-acquisition financial statements; and 2) Calculated borrowing costs based on the funding status, credit ratings and debt/equity ratios of the Group after the business combination.

Disposal of Subsidiaries

Disposal of Subsidiaries	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Disposal of Subsidiaries	31. DISPOSAL OF SUBSIDIARIES The Group disposed of its subsidiary Kun Shan Ding Yue Real Estate Development Co., Ltd. (“KSDY”), in June 2017 and, as a result, the Group lost its control over KSDY. a. Gain on disposal of subsidiaries NT$ Total consideration $ 7,046,464 Net assets disposed of (1,457,007 ) Gain on disposal of KSDY $ 5,589,457 b. Analysis of assets and liabilities on the date control was lost NT$ Current assets Cash and cash equivalents $ 29,133 Inventories related to real estate business 1,427,874 Net assets disposed of $ 1,457,007

Equity Transaction with Non-con

Equity Transaction with Non-controlling Interests	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Equity Transaction with Non-controlling Interests	32. EQUITY TRANSACTION WITH NON-CONTROLLING INTERESTS In February 2016, USIE repurchased its own 4,501 thousand outstanding ordinary shares and, as a result, the Group’s shareholdings of USIE increased from 96.7% to 98.8%. The transaction was accounted for as an equity transaction since the Group did not cease to have control over USIE and capital surplus was decreased by NT$1,912,887 thousand in 2016. In February 2016, the Company disposed 39,603 thousand shares in USI to the Company’s subsidiary, UGTW, at NT$20 per share with a total consideration of NT$792,064 thousand and, as a result, the Group’s shareholdings of USI decreased from 99.0% to 76.5%. The transaction was accounted for as an equity transaction since the Group did not cease to have control over USI and capital surplus was decreased by NT$20,552 thousand in 2016. In January 2017, USI completed its cash capital increase of NT$1,000,000 thousand and the Group’s shareholdings of USI increased from 75.2% to 75.7% since the Group did not proportionally subscribe for additional new shares. The transaction was accounted for as an equity transaction since the transaction did not change the Company’s control over USI and capital surplus was increased by NT$3,055 thousand in 2017. In January 2018, the shareholders’ meeting of USIE resolved to repurchase its own outstanding 3,738 thousand ordinary shares at US$17.49 per share and, as a result, the Group’s shareholdings of USIE increased from 96.9% to 98.6%. The transaction was accounted for as an equity transaction since the transaction did not change the Company’s control over USIE and capital surplus was decreased by NT$1,127,632 thousand (US$36,839 thousand) in the first quarter of 2018. In February 2018, the board of directors of USIE resolved February 26, 2018 was the record date for capital reduction and then the repurchased ordinary shares were subsequently cancelled. In March 2018, ASE’s board of directors resolved to sign the shares transfer agreement by its subsidiary, J&R Holding, for acquiring shares of ASEN from NXP B.V. at US$127,113 thousand (NT$3,871,862 thousand). As a result, the percentage of ownership in ASEN was increased from 60% to 100%. The transaction was accounted for as an equity transaction since the transaction did not change the Company’s control over ASEN and capital surplus was decreased by NT$1,737,315 thousand (US$56,756 thousand) in the third quarter of 2018. In August 2018, J&R Holding’s board of directors further resolved to sell 30% shareholdings of ASEN to Tsinghua Unigroup Ltd. at US$95,335 thousand. As a result, the Group’s shareholdings of ASEN was decreased from 100% to 70%. The transaction was accounted for as an equity transaction since the Group also did not cease to have control over ASEN and capital surplus was increased by NT$1,114,504 thousand (US$36,410 thousand) in the fourth quarter of 2018. In July 2018, ASE and UGTW’s board of directors have approved to acquire the outstanding ordinary shares of USIINC and USI at NT$35 (US$1.1) and NT$18 (US$0.6) per ordinary shares, respectively. ASE and UGTW also purchased the ordinary shares from dissenting shareholders in August 2018 and recognized an increase in capital surplus by NT$9,530 thousand (US$311 thousand). ASE has completed the acquisition of USIINC’s remaining outstanding ordinary shares and recognized a decrease in capital surplus by NT$28,152 thousand (US$920 thousand).

Cash Flows Information

Cash Flows Information	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Cash Flows Information	33. CASH FLOWS INFORMATION a. Non-cash investing activities In addition to Notes 22, 25 and 30, the Group entered into the following non-cash investing activities which were not reflected in the consolidated statements of cash flows for the years ended December 31, 2016, 2017 and 2018: For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Payments for property, plant and equipment Purchase of property, plant and equipment $ 27,680,862 $ 23,677,682 $ 39,092,238 $ 1,277,107 For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Increase (decrease) in prepayments for property, plant and equipment $ (89,337 ) $ 90,560 $ 402,255 $ 13,141 Decrease (increase) in payables for property, plant and equipment (823,171 ) 982,260 1,942,259 63,452 Capitalized borrowing costs (54,191 ) (51,262 ) (50,309 ) (1,643 ) $ 26,714,163 $ 24,699,240 $ 41,386,443 $ 1,352,057 Proceeds from disposal of property, plant and equipment Consideration from disposal of property, plant and equipment $ 692,826 $ 1,487,334 $ 1,133,435 $ 37,028 Decrease (increase) in other receivables (22,626 ) 876 (5,791 ) (189 ) $ 670,200 $ 1,488,210 $ 1,127,644 $ 36,839 Payments for investment properties Purchase of investment properties $ - $ 186,535 $ 125,853 $ 4,112 Capitalized borrowing costs - (13 ) (89 ) (3 ) $ - $ 186,522 $ 125,764 $ 4,109 Payments for other intangible assets Purchase of other intangible assets $ 675,144 $ 277,825 $ 537,659 $ 17,565 Decrease (increase) in other payables (120,938 ) 60,159 40,106 1,310 Increase in other non-current liabilities (40,313 ) - - - $ 513,893 $ 337,984 $ 577,765 $ 18,875 Net cash inflow from disposal of subsidiaries Consideration from disposal of subsidiaries $ - $ 7,046,464 $ - $ - Increase in other payables - 3,552 - - Cash and cash equivalents disposed of - (29,133 ) - - $ - $ 7,020,883 $ - $ - b. Changes in liabilities arising from financing activities For the year ended December 31, 2017 Short-term borrowings Bonds payable Long-term borrowings Total NT$ NT$ NT$ NT$ Balance at January 1, 2017 $ 20,955,522 $ 36,999,903 $ 53,115,563 $ 111,070,988 Financing cash flows (2,038,993 ) (1,123,972 ) (16,473,381 ) (19,636,346 ) Non-cash changes Bonds conversion - (11,650,369 ) - (11,650,369 ) Amortization of issuance cost - 319,463 5,790 325,253 Effects of exchange rate change (954,058 ) (1,402,245 ) (1,241,344 ) (3,597,647 ) Balance at December 31, 2017 $ 17,962,471 $ 23,142,780 $ 35,406,628 $ 76,511,879 For the year ended December 31, 2018 Short-term borrowings Bonds payable Long-term borrowings Total NT$ NT$ NT$ NT$ Balance at January 1, 2018 $ 17,962,471 $ 23,142,780 $ 35,406,628 $ 76,511,879 Financing cash flows 22,327,813 (6,185,600 ) 85,510,959 101,653,172 Non-cash changes Acquisition through business combinations (Note 30) 3,619,858 4,457,191 16,080,125 24,157,174 Bonds conversion - (4,457,191 ) - (4,457,191 ) Reclassification for applying IFRS 9 (1,301,994 ) - - (1,301,994 ) Amortization of issuance cost - 28,756 188,217 216,973 Effects of foreign currency exchange 655,321 - 712,400 1,367,721 Balance at December 31, 2018 $ 43,263,469 $ 16,985,936 $ 137,898,329 $ 198,147,734 Short-term borrowings Bonds payable Long-term borrowings Total US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) Balance at January 1, 2018 $ 586,817 $ 756,053 $ 1,156,701 $ 2,499,571 Financing cash flows 729,429 (202,078 ) 2,793,563 3,320,914 Non-cash changes Acquisition through business combinations (Note 30) 118,257 145,612 525,323 789,192 Bonds conversion - (145,612 ) - (145,612 ) Reclassification for applying IFRS 9 (42,535 ) - - (42,535 ) Amortization of issuance cost - 940 6,149 7,089 Effects of foreign currency exchange 21,409 - 23,273 44,682 Balance at December 31, 2018 $ 1,413,377 $ 554,915 $ 4,505,009 $ 6,473,301

Operating Lease Arrangements

Operating Lease Arrangements	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Operating Lease Arrangements	34. OPERATING LEASE ARRANGEMENTS a. The Group as lessee In addition to those disclosed in Note 20, the Company and some of its subsidiary located in R.O.C. lease the land on which their buildings are located under various operating lease agreements with the R.O.C. government expiring through January 2037. The agreements grant these entities the option to renew the leases and reserve the right for the lessor to adjust the lease payments upon an increase in the assessed value of the land and to terminate the leases under certain conditions. In addition, the Group leases buildings, machinery and equipment under operating leases. The subsidiaries’ offices located in U.S.A. and Japan, etc. are leased from third parties and the lease terms will expire through 2019 to 2028 with the option to renew the leases upon expiration. The Group recognized rental expense of NT$1,411,533 thousand, NT$1,193,477 thousand and NT$ 1,593,315 thousand (US$52,052 thousand) for the years ended December 31, 2016, 2017 and 2018, respectively, from the aforementioned operating lease arrangements and the land use rights disclosed in Note 20. The future minimum lease payments of non-cancellable operating lease agreements were as follows: December 31 2017 2018 NT$ NT$ US$ (Note 4) Less than 1 year $ 246,026 $ 509,994 $ 16,661 1-5 years 439,408 828,482 27,066 More than 5 years 419,232 1,047,626 34,225 $ 1,104,666 $ 2,386,102 $ 77,952 b. The Group as lessor The Group leased out the investment properties under operating lease with leasing periods from 1 to 15 years. The Group granted lessees the option to renew the lease upon expiration and without bargain purchase. The future minimum lease payments of non-cancellable operating lease agreements were as follows: December 31, 2018 NT$ US$ (Note 4) Less than 1 year $ 916,891 $ 29,954 1-5 years 2,391,843 78,139 More than 5 years 1,157,093 37,801 $ 4,465,827 $ 145,894

Capital Management

Capital Management	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Capital Management	35. CAPITAL MANAGEMENT The capital structure of the Group consists of debt and equity. The Group manages its capital to ensure that entities in the Group will be able to continue as going concerns while maximizing the return to shareholders through the optimization of the debt and equity balance. Key management personnel of the Group periodically reviews the cost of capital and the risks associated with each class of capital. In order to balance the overall capital structure, the Group may adjust the amount of dividends paid to shareholders, the number of new shares issued or repurchased, and the amount of new debt issued or existing debt redeemed. The Group is not subject to any externally imposed capital requirements except those discussed in Note 21.

Financial Instruments

Financial Instruments	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Financial Instruments	36. FINANCIAL INSTRUMENTS a. Fair value of financial instruments that are not measured at fair value 1) Fair value of financial instruments not measured at fair value but for which fair value is disclosed Except bonds payable measured at amortized cost, the management considered that the carrying amounts of financial assets and financial liabilities not measured at fair value approximate their fair values. The carrying amounts and fair value of bonds payable as of December 31, 2017 and 2018, respectively, were as follows: Carrying Amount Fair Value NT$ US$ (Note 4) NT$ US$ (Note 4) December 31, 2017 $ 23,142,780 $ 23,247,085 December 31, 2018 16,985,936 $ 554,915 17,126,752 $ 559,515 2) Fair value hierarchy The aforementioned fair value hierarchy of bonds payable was Level 3 which was determined based on discounted cash flow analysis with the applicable yield curve for the duration or the latest trading prices. The significant unobservable inputs is discount rates that reflected the credit risk of various counterparties and the latest trading prices. b. Fair value of financial instruments that are measured at fair value on a recurring basis 1) Fair value hierarchy Level 1 Level 2 Level 3 Total NT$ NT$ NT$ NT$ December 31, 2017 Financial assets at FVTPL Financial assets designated as at FVTPL Private-placement convertible bonds $ - $ 100,496 $ - $ 100,496 Derivative financial assets Forward exchange contracts - 61,325 - 61,325 Swap contracts - 60,538 - 60,538 Non-derivative financial assets held for trading Quoted ordinary shares 4,410,732 - - 4,410,732 Open-end mutual funds 589,976 - - 589,976 $ 5,000,708 $ 222,359 $ - $ 5,223,067 Available-for-sale financial assets Unquoted ordinary shares $ - $ - $ 662,477 $ 662,477 Limited Partnership - - 246,072 246,072 Quoted ordinary shares 279,791 - - 279,791 Open-end mutual funds 23,825 - - 23,825 $ 303,616 $ - $ 908,549 $ 1,212,165 Level 1 Level 2 Level 3 Total NT$ NT$ NT$ NT$ Financial liabilities at FVTPL Derivative financial liabilities Swap contracts $ - $ 652,107 $ - $ 652,107 Forward exchange contracts - 25,323 - 25,323 $ - $ 677,430 $ - $ 677,430 Level 1 Level 2 Level 3 Total NT$ US$ (Note 4) NT$ US$ (Note 4) NT$ US$ (Note 4) NT$ US$ (Note 4) December 31, 2018 Financial assets at FVTPL Derivative financial assets Swap contracts $ - $ - $ 1,557,714 $ 50,889 $ - $ - $ 1,557,714 $ 50,889 Forward exchange contracts - - 32,070 1,048 - - 32,070 1,048 Non-derivative financial assets Quoted ordinary shares 5,151,255 168,287 - - - - 5,151,255 168,287 Open-end mutual funds 581,800 19,007 - - - - 581,800 19,007 Unquoted preferred shares - - - - 275,000 8,984 275,000 8,984 Private-placement funds - - - - 200,123 6,537 200,123 6,537 Hybrid financial assets Private-placement convertible bonds - - 100,496 3,283 - - 100,496 3,283 $ 5,733,055 $ 187,294 $ 1,690,280 $ 55,220 $ 475,123 $ 15,521 $ 7,898,458 $ 258,035 Financial assets at FVTOCI Investments in equity instruments Unquoted shares $ - $ - $ - $ - $ 540,730 $ 17,665 $ 540,730 $ 17,665 Limited partnership - - - - 39,669 1,296 39,669 1,296 Investments in debt instruments Unsecured subordinate corporate bonds - - - - 1,016,924 33,222 1,016,924 33,222 $ - $ - $ - $ - $ 1,597,323 $ 52,183 $ 1,597,323 $ 52,183 Financial liabilities at FVTPL Derivative financial liabilities Swap contracts $ - $ - $ 29,058 $ 949 $ - $ - $ 29,058 $ 949 Forward exchange contracts - - 7,597 248 - - 7,597 248 $ - $ - $ 36,655 $ 1,197 $ - $ - $ 36,655 $ 1,197 For the financial assets and liabilities that were measured at fair value on a recurring basis held for the years ended December 31, 2017 and 2018, there were no transfers between Level 1 and Level 2 of the fair value hierarchy. 2) Reconciliation of Level 3 fair value measurements of financial assets For the years ended December 31, 2016 and 2017 For the Year Ended December 31 2016 2017 NT$ NT$ Balance at January 1 $ 741,089 $ 904,790 Purchases 495,928 2,649 Total gain or loss In profit or loss (100,734 ) 28 In other comprehensive income (202,565 ) 17,284 Disposals (28,928 ) (16,202 ) Balance at December 31 $ 904,790 $ 908,549 For the year ended December 31, 2018 FVTPL FVTOCI Financial Assets Equity Instruments Equity Instruments Debt Instruments Total NT$ US$ (Note 4) NT$ US$ (Note 4) NT$ US$ (Note 4) NT$ US$ (Note 4) Balance at January 1 (Note 3) $ - $ - $ 908,549 $ 29,681 $ 1,080,000 $ 35,283 $ 1,988,549 $ 64,964 Recognized in profit or loss (2,313 ) (76 ) - - - - (2,313 ) (76 ) Recognized in other comprehensive income (included in unrealized losses on financial assets at FVTOCI) - - (224,172 ) (7,323 ) (63,076 ) (2,061 ) (287,248 ) (9,384 ) Purchases 477,436 15,597 105,000 3,430 - - 582,436 19,027 Disposals - - (208,978 ) (6,827 ) - - (208,978 ) (6,827 ) Balance at December 31 $ 475,123 $ 15,521 $ 580,399 $ 18,961 $ 1,016,924 $ 33,222 $ 2,072,446 $ 67,704 3) Valuation techniques and assumptions applied for the purpose of measuring fair value a) Valuation techniques and inputs applied for the purpose of measuring Level 2 fair value measurement Financial Instruments Valuation Techniques and Inputs Derivatives - swap contracts and forward exchange contracts Discounted cash flows - Future cash flows are estimated based on observable forward exchange rates at balance sheet dates and contract forward exchange rates, discounted at rates that reflected the credit risk of various counterparties. Private-placement convertible bonds Discounted cash flows - Future cash flows are estimated based on observable stock prices at balance sheet dates and contract conversion prices, discounted at rates that reflected the credit risk of various counterparties. b) Valuation techniques and inputs applied for the purpose of measuring Level 3 fair value measurement The fair value of unquoted ordinary shares and private-placement funds were determined using market approach and asset-based approach. The significant unobservable inputs is the discount for lack of marketability of 20% to 30% . The fair values of investments in limited partnership are measured by estimating future cash inflows from disposal (net of transaction cost). The fair values of the unsecured subordinate corporate bonds were determined using income approach based on a discounted cash flow analysis. The significant unobservable input is the discount rate that reflects the credit risk of the counterparty. If the discount rate c. Categories of financial instruments December 31 2017 2018 NT$ NT$ US$ (Note 4) Financial assets FVTPL Designated as at FVTPL $ 100,496 $ - $ - Held for trading 5,122,571 - - Mandatorily at FVTPL - 7,898,458 258,035 Available-for-sale financial assets 1,212,165 - - Loans and receivables (Note 1) 103,973,567 - - Measured at amortized cost (Note 1) - 139,866,736 4,569,314 FVTOCI Equity instruments - 580,399 18,961 Debt instruments - 1,016,924 33,222 Financial liabilities FVTPL Held for trading 677,430 36,655 1,197 Financial liabilities for hedging - 3,899,634 127,397 Measured at amortized cost (Note 2) 139,561,999 286,035,732 9,344,520 Note 1: The balances included financial assets measured at amortized cost which comprise cash and cash equivalents, trade and other receivables and other financial assets. Note 2: The balances included financial liabilities measured at amortized cost which comprise short-term borrowings, trade and other payables, bonds payable and long-term borrowings. d. Financial risk management objectives and policies The derivative instruments used by the Group are to mitigate risks arising from ordinary business operations. All derivative transactions entered into by the Group are designated as either hedging or trading. Derivative transactions entered into for hedging purposes must hedge risk against fluctuations in foreign exchange rates and interest rates arising from operating activities. The currencies and the amount of derivative instruments held by the Group must match its hedged assets and liabilities denominated in foreign currencies. The Group’s risk management department monitors risks to mitigate risk exposures, reports unsettled position, transaction balances and related gains or losses to the Group’s chief financial officer on monthly basis. 1) Market risk The Group’s activities exposed it primarily to the financial risks of changes in foreign currency exchange rates and interest rates. Gains or losses arising from fluctuations in foreign currency exchange rates of a variety of derivative financial instruments were approximately offset by those of hedged items. Interest rate risk was not significant due to the cost of capital was expected to be fixed. There had been no change to the Group’s exposure to market risks or the manner in which these risks were managed and measured. a) Foreign currency exchange rate risk The Group had sales and purchases as well as financing activities denominated in foreign currency which exposed the Group to foreign currency exchange rate risk. The Group entered into a variety of derivative financial instruments to hedge foreign currency exchange rate risk to minimize the fluctuations of assets and liabilities denominated in foreign currencies. The carrying amounts of the Group’s foreign currency denominated monetary assets and liabilities (including those eliminated upon consolidation) as well as derivative instruments which exposed the Group to foreign currency exchange rate risk at each balance sheet date are presented in Note 40. The Group was principally subject to the impact to exchange rate fluctuation in US$ and JPY against NT$ or CNY. 1% is the sensitivity rate used when reporting foreign currency exchange rate risk internally to key management personnel and represents management’s assessment of the reasonably possible change in foreign currency exchange rates. The sensitivity analysis included financial assets and liabilities and inter-company receivables and payables within the Group. The changes in profit before income tax due to a 1% change in U.S. dollars and Japanese yen both against NT$ and CNY would be NT$69,000 thousand, NT$101,000 thousand and NT$129,000 thousand (US$4,214 thousand) for the years ended December 31, 2016, 2017 and 2018, respectively. Hedging contracts and hedged items have been taken into account while measuring the changes in profit before income tax. The abovementioned sensitivity analysis mainly focused on the foreign currency monetary items at the end of the year. As the year-end exposure did not reflect the exposure for the years ended December 31, 2016, 2017 and 2018, the abovementioned sensitivity analysis was unrepresentative of those years. Hedge accounting-2018 The Group’s hedging strategy is to lift foreign currency borrowings to avoid 100% exchange rate exposure of its foreign currency equity instruments, which is designated as fair value hedges. Hedge adjustments are made when the foreign currency equity instruments were evaluated based on the exchange rates on each balance sheet date, the foreign exchange gains (losses) will be totally offset. The source of hedge ineffectiveness in these hedging relationships is the material difference between the notional amounts of foreign currency borrowings and foreign currency equity instruments. No other sources of ineffectiveness is expected to emerge from these hedging relationships. b) Interest rate risk Except a portion of long-term borrowings and bonds payable at fixed interest rates, the Group was exposed to interest rate risk because group entities borrowed funds at floating interest rates. Changes in market interest rates will lead to variances in effective interest rates of borrowings from which the future cash flow fluctuations arise. The Group uses financing tool with low interest rate and favorable term so as to maintain low financing cost, adequate banking facilities, as well as to hedge interest rate risk. The carrying amounts of the Group’s financial assets and financial liabilities with exposure to interest rates at each balance sheet date were as follows: December 31 2017 2018 NT$ NT$ US$ (Note 4) Fair value interest rate risk Financial liabilities $ 17,552,955 $ 17,485,561 $ 571,237 Cash flow interest rate risk Financial assets 39,880,736 32,942,747 1,076,209 Financial liabilities 42,270,321 172,737,393 5,643,169 For assets and liabilities with floating interest rates, a 100 basis point increase or decrease was used when reporting interest rate risk internally to key management personnel. If interest rates had been 100 basis points (1%) higher or lower and all other variables held constant, the Group’s profit before income tax for the years ended December 31, 2016, 2017 and 2018 would have decreased or increased approximately by NT$358,000 thousand, NT$24,000 thousand and NT$1,398,000 thousand (US$45,671 thousand), respectively. Hedging contracts and hedged items have been taken into account while measuring the changes in profit before income tax. The abovementioned sensitivity analysis mainly focused on the interest rate items at the end of the reporting period. As the year-end exposure did not reflect the exposure for the years ended December 31, 2016, 2017 and 2018, the abovementioned sensitivity analysis was unrepresentative of those periods. c) Other price risk The Group was exposed to equity or bond price risk through its investments in financial assets at FVTPL (included quoted ordinary shares, open-end mutual funds, unquoted preferred shares, private-placement funds and private-placement convertible bonds) and financial assets at FVTOCI for the year ended December 31, 2018. If equity and bond prices were 1% higher or lower, profit before income tax for the year ended December 31, 2018 would have increased or decreased approximately by NT$64,000 thousand (US$2,091 thousand) and other comprehensive income before income tax for the year ended December 31, 2018 would have increased or decreased approximately by NT$16,000 thousand (US$523 thousand). ASE and its subsidiaries were exposed to equity or debt price risk through its investments in financial assets at FVTPL (including private-placement convertible bonds, quoted shares and open-end mutual funds) and available-for-sale financial assets for the years ended December 31, 2016 and 2017. If equity or debt prices were 1% higher or lower, profit before income tax for the years ended December 31, 2016 and 2017 would have increased or decreased approximately by NT$26,000 thousand and NT$52,000 thousand, respectively, and other comprehensive income before income tax for the years ended December 31, 2016 and 2017 would have both increased or decreased approximately by NT$13,000 thousand. In addition, ASE was also exposed to its ordinary share price risk through conversion option, redemption option and put option of Bonds which was recognized as financial liabilities held for trading as of December 31, 2016. 7% is the sensitivity rate used when reporting price risk internally to key management personnel. If the ASE’s ordinary share price increased or decreased by 7%, profit before income tax for the year ended December 31, 2016 would have decreased approximately by NT$510,000 thousand or increased approximately by NT$445,000 thousand. 2) Credit risk Credit risk refers to the risk that counterparty will default on its contractual obligations resulting in financial loss to the Group. The Group’s credit risk arises from cash and cash equivalents, trade and other receivables and other financial assets. The Group’s maximum exposure to credit risk was the carrying amounts of financial assets in the consolidated balance sheets. As of December 31, 2017 and 2018, the Group’s five largest customers accounted for 33% and 36% of trade receivables, respectively. The Group transacts with a large number of unrelated customers and, thus, no concentration of credit risk was observed. 3) Liquidity risk The Group manages liquidity risk by maintaining adequate working capital and banking facilities to fulfill the demand for cash flow used in the Group’s operation and capital expenditure. The Group also monitors its compliance with all the loan covenants. Liquidity risk is not considered to be significant. In the table below, financial liabilities with a repayment on demand clause were included in the earliest time band regardless of the probability of counter-parties choosing to exercise their rights. The maturity dates for other non-derivative financial liabilities were based on the agreed repayment dates. To the extent that interest flows are floating rate, the undiscounted amounts were derived from the interest rates at each balance sheet date. On Demand or Less than 1 Month 1 to 3 Months 3 Months to 1 Year 1 to 5 Years More than 5 Years NT$ NT$ NT$ NT$ NT$ December 31, 2017 Non-derivative financial liabilities Non-interest bearing $ 30,695,797 $ 18,387,296 $ 4,549,468 $ 2,807 $ 176,199 Floating interest rate liabilities 6,641,541 4,153,830 5,101,178 27,196,245 900,310 Fixed interest rate liabilities 8,522,765 7,526,270 1,526,449 11,902,335 6,462,396 $ 45,860,103 $ 30,067,396 $ 11,177,095 $ 39,101,387 $ 7,538,905 December 31, 2018 Non-derivative financial liabilities Non-interest bearing $ 33,156,044 $ 34,493,000 $ 6,899,093 $ 57,375 $ 196,523 Floating interest rate liabilities 15,762,004 7,127,606 25,510,718 131,014,040 - Fixed interest rate liabilities 7,677,097 4,811,536 242,461 13,621,814 4,367,546 $ 56,595,145 $ 46,432,142 $ 32,652,272 $ 144,693,229 $ 4,564,069 On Demand or Less than 1 Month 1 to 3 Months 3 Months to 1 Year 1 to 5 Years More than 5 Years US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) December 31, 2018 Non-derivative financial liabilities Non-interest bearing $ 1,083,177 $ 1,126,854 $ 225,387 $ 1,874 $ 6,420 Floating interest rate liabilities 514,930 232,852 833,411 4,280,106 - Fixed interest rate liabilities 250,804 157,188 7,921 445,012 142,684 $ 1,848,911 $ 1,516,894 $ 1,066,719 $ 4,726,992 $ 149,104 The amounts included above for floating interest rate instruments for non-derivative financial liabilities was subject to change if changes in floating interest rates differ from those estimates of interest rates determined at each balance sheet date. The following table detailed the Group’s liquidity analysis for its derivative financial instruments. The table was based on the undiscounted contractual net cash inflows and outflows on derivative instruments that settle on a net basis, and the undiscounted gross cash inflows and outflows on those derivatives that require gross settlement. When the amounts payable or receivable are not fixed, the amounts disclosed have been determined by reference to the projected interest rates as illustrated by the yield curves at each balance sheet date. On Demand or Less than 1 Month 1 to 3 Months 3 Months to 1 Year NT$ NT$ NT$ December 31, 2017 Net settled Forward exchange contracts $ (8,820 ) $ - $ - Gross settled Forward exchange contracts Inflows $ 3,711,302 $ 2,169,093 $ 390,379 Outflows (3,679,154 ) (2,138,635 ) (386,880 ) 32,148 30,458 3,499 Swap contracts Inflows 12,116,531 14,434,880 36,676,224 Outflows (12,189,576 ) (14,629,738 ) (36,452,398 ) (73,045 ) (194,858 ) 223,826 $ (40,897 ) $ (164,400 ) $ 227,325 December 31, 2018 Net settled Forward exchange contracts $ 2,040 $ 1,620 $ - Gross settled Forward exchange contracts Inflows $ 2,580,194 $ 466,489 $ - Outflows (2,556,607 ) (460,725 ) - 23,587 5,764 - Swap contracts Inflows Outflows 14,136,620 9,214,500 38,160,316 (13,946,583 ) (8,650,320 ) (36,596,419 ) 190,037 564,180 1,563,897 $ 213,624 $ 569,944 $ 1,563,897 On Demand or Less than 1 Month 1 to 3 Months 3 Months to 1 Year US$ (Note 4) US$ (Note 4) US$ (Note 4) December 31, 2018 Net settled Forward exchange contracts $ 67 $ 53 $ - On Demand or Less than 1 Month 1 to 3 Months 3 Months to 1 Year US$ (Note 4) US$ (Note 4) US$ (Note 4) Gross settled Forward exchange contracts Inflows $ 84,293 $ 15,240 $ - Outflows (83,522 ) (15,052 ) - 771 188 - Swap contracts Inflows 461,830 301,029 1,246,662 Outflows (455,622 ) (282,598 ) (1,195,571 ) 6,208 18,431 51,091 $ 6,979 $ 18,619 $ 51,091

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Related Party Transactions	37. RELATED PARTY TRANSACTIONS Balances and transactions within the Group had been eliminated upon consolidation. Details of transactions between the Group and other related parties were disclosed as follows: a. Related parties In addition to those disclosed in Note 15, the related parties were as follows: Related Parties Relationship with the Company ASE Cultural and Educational Foundation Substantial related party Fu Hwa Construction Co., Ltd. Associate’s subsidiary b. The Group contributed NT$100,000 thousand (US$3,267 thousand) to ASE Cultural and Educational Foundation in 2016, 2017 and 2018, respectively, for environmental charity in promoting the related domestic environmental protection and public service activities (Note 39). c. In the third quarter of 2016, the Group acquired patents and specific technology from DECA at NT$403,543 thousand, which was primarily based on independent professional appraisal reports. As of December 31, 2017 and 2018, NT$93,000 thousand and NT$57,590 thousand (US$1,881 thousand) have not been paid and were accrued under the line item of other payables, respectively. d. The Group contracted with Fu Hwa Construction Co., Ltd. to construct a female employee dormitory on current leased land. Total consideration was primarily based on independent professional appraisal reports. During 2016, the employee dormitory has been capitalized for NT$875,000 thousand. The female employee dormitory has been completely constructed in 2016. As of December 31, 2016, NT$228,500 thousand has not been paid and was accrued under the line item of other payables, which was fully repaid in March 2017. e. In February 2016, USIE repurchased 1,801 thousand shares of USIE’s outstanding ordinary shares from the Group’s key management personnel with approximately NT$1,130,650 thousand. f. As disclosed in Note 32, the Company’s subsidiary, USIE, repurchased its own 1,283 thousand ordinary shares from the Group’s key management personnel in February 2018 with approximately NT$ 653,244 thousand (US$21,341 thousand). g. Compensation to key management personnel For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Short-term employee benefits $ 790,460 $ 860,631 $ 1,041,216 $ 34,015 Post-employment benefits 4,790 2,858 3,884 127 Share-based payments 11,547 - 9,145 299 $ 806,797 $ 863,489 $ 1,054,245 $ 34,441 The compensation to the Group’s key management personnel is determined according to personal performance and market trends.

Assets Pledged as Collateral or

Assets Pledged as Collateral or for Security	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Assets Pledged as Collateral or for Security	38. ASSETS PLEDGED AS COLLATERAL OR FOR SECURITY The following assets were provided as collateral for bank borrowings and the tariff guarantees of imported raw materials: December 31 2017 2018 NT$ NT$ US$ (Note 4) Inventories related to real estate business $ 4,822,043 $ 4,796,126 $ 156,685 Investment properties 7,151,382 6,680,017 218,230 Land use rights (long-term prepayments for lease) 6,813,751 6,515,576 212,858 Other financial assets (including current and non-current) 66,726 496,902 16,233 $ 18,853,902 $ 18,488,621 $ 604,006

Significant Contingent Liabilit

Significant Contingent Liabilities and Unrecognized Commitments	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Significant Contingent Liabilities and Unrecognized Commitments	39. SIGNIFICANT CONTINGENT LIABILITIES AND UNRECOGNIZED COMMITMENTS In addition to those disclosed in other notes, significant commitments and contingencies of the Group as of each balance sheet date were as follows: a. As of December 31, 2017 and 2018, unused letters of credit of the Group were approximately NT$20,000 thousand and NT$634,000 thousand (US$20,712 thousand), respectively. b. As of December 31, 2017 and 2018, outstanding commitments to purchase property, plant and equipment of the Group were approximately NT$7,019,377 thousand and NT$17,039,458 thousand (US$556,663 thousand), respectively, of which NT$294,194 thousand and NT$2,339,308 thousand (US$76,423 thousand) had been prepaid, respectively. As of December 31, 2017 and 2018, the commitment that the Group has contracted for the construction related to our real estate business were approximately NT$1,548,806 thousand and NT$888,052 thousand (US$29,012 thousand), respectively. c. In consideration of corporate social responsibility for environmental protection, the Group’s board of directors, in December 2013, approved contributions to be made in the next 30 years, at a total amount of NT$3,000,000 thousand, at the minimum, to environmental protection efforts in Taiwan. In February 2019, the Group’s board of directors approved to contribute NT$100,000 thousand (US$3,267 thousand) to ASE Cultural & Educational Foundation for environmental charity in promoting the related domestic environmental protection and public service activities continuously.

Significant Subsequent Events

Significant Subsequent Events	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Significant Subsequent Events	40. SIGNIFICANT SUBSEQUENT EVENTS On March 28, 2019, the Company’s board of directors resolved to issue ordinary shares in the way of cash capital increase in an amount up to NT$3,000,000 thousand (US$98,007 thousand) with par value NT$10 (US$0.3) per share. The Company’s board of directors also resolved to issue unsecured domestic bonds that were approved by the Taipei Exchange. These bonds will be issued in the amounts of NT$6,500,000 thousand (US$212,349 thousand) and NT$3,500,000 thousand (US$114,342 thousand) with annual interest rates of 0.9% and 1.03%, respectively, and with maturity of 5 and 7 years, respectively.

Significant Assets and Liabilit

Significant Assets and Liabilities Denominated in Foreign Currencies	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Significant Assets and Liabilities Denominated in Foreign Currencies	41. SIGNIFICANT ASSETS AND LIABILITIES DENOMINATED IN FOREIGN CURRENCIES The following information was aggregated by the foreign currencies other than functional currencies of the group entities and the exchange rates between foreign currencies and respective functional currencies were disclosed. The significant financial assets and liabilities denominated in foreign currencies were as follows: Foreign Currencies (In Thousand) Exchange Rate Carrying Amount (In Thousand) December 31, 2017 Monetary financial assets US$ $ 3,065,296 US$1=NT$29.76 $ 91,223,195 US$ 1,193,369 US$1=CNY6.5342 35,514,653 JPY 5,005,435 JPY1=NT$0.2642 1,322,436 JPY 8,113,284 JPY1=US$0.0089 2,143,530 Monetary financial liabilities US$ 2,902,995 US$1=NT$29.76 86,393,137 US$ 1,007,629 US$1=CNY6.5342 29,987,042 JPY 5,415,677 JPY1=NT$0.2642 1,430,822 JPY 8,598,832 JPY1=US$0.0089 2,271,811 December 31, 2018 Monetary financial assets US$ 3,730,484 US$1=NT$30.715 114,581,814 US$ 1,299,391 US$1=CNY6.8632 39,910,801 JPY 4,412,591 JPY1=NT$0.2782 1,227,583 JPY 6,568,657 JPY1=US$0.0091 1,827,400 Monetary financial liabilities US$ 3,361,523 US$1=NT$30.715 103,249,185 US$ 1,216,654 US$1=CNY6.8632 37,369,521 JPY 7,401,621 JPY1=NT$0.2782 2,059,131 JPY 7,035,704 JPY1=US$0.0091 1,957,333 The significant realized and unrealized foreign exchange gain (loss) were as follows: For the Year Ended December 31 2016 2017 2018 Functional Exchange Rate Net Foreign Exchange Gain Exchange Rate Net Foreign Exchange Gain (Loss) Exchange Rate Net Foreign Exchange Loss NT$ NT$ NT$ US$ (Note 4) NT$ $ 1,494,044 $ 4,130,243 $ (849,234 ) $ (27,744 ) US$ US$1=NT$32.25 203,258 US$1=NT$29.76 (244,802 ) US$1=NT$30.715 (67,476 ) (2,204 ) CNY CNY1=NT$4.649 224,393 CNY1=NT$4.5545 (337,630 ) CNY1=NT$4.4753 (120,005 ) (3,920 ) $ 1,921,695 $ 3,547,811 $ (1,036,715 ) $ ($33,868)

Others

Others	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Others	42. OTHERS On December 20, 2013, the Kaohsiung Environmental Protection Bureau (“KEPB”) imposed a fine of NT$102,014 thousand (“the Administrative Fine”) upon the Company for the violation of the Water Pollution Control Act. The Company filed an administrative appeal to nullify the Administrative Fine, which, however, was dismissed by the Kaohsiung City Government. The Company then filed a lawsuit with the Kaohsiung High Administrative Court seeking to revoke the dismissal decision made by the Kaohsiung City Government (the “Administrative Appeal Decision”) and the Administrative Fine, and to demand a refund of the fine paid by the Company. The judgment of the Kaohsiung High Administrative Court was rendered on March 22, 2016, ruling to revoke the Administrative Appeal Decision and the Administrative Fine, and to dismiss the other complaint filed by the Company (i.e., to demand a refund of the fine paid by the Company). The Company appealed against the unfavorable ruling on April 14, 2016. On June 8, 2017, the Supreme Administrative Court handed down a final and unappealable judgment which is in favor of the Company and ordered KEPB to return to the Company the fine already paid by the Company.

Operating Segments Information

Operating Segments Information	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Operating Segments Information	43. OPERATING SEGMENTS INFORMATION The Group has the following reportable segments: Packaging, Testing and EMS. The Group packages bare semiconductors into finished semiconductors with enhanced electrical and thermal characteristics; provides testing services, including front-end engineering testing, wafer probing and final testing services; engages in the designing, assembling, manufacturing and sale of electronic components and telecommunications equipment motherboards. Information about other business activities and operating segments that are not reportable are combined and disclosed in “Others.” The Group engages in other activities such as substrate production as well as sale and leasing of real estate properties. The accounting policies for segments are the same as those described in Note 4. The measurement basis for resources allocation and performance evaluation is based on profit before income tax. Segment information for the years ended December 31, 2016, 2017 and 2018 was as follows: a. Segment revenues and operation results Adjustments Packaging Testing EMS Others and Eliminations Total NT$ NT$ NT$ NT$ NT$ NT$ For the year ended December 31, 2016 Revenue from external customers $ 125,282,829 $ 27,031,750 $ 115,395,130 $ 7,174,398 $ - $ 274,884,107 Inter-segment revenue (Note 1) 4,929,897 243,980 47,721,424 9,186,359 (62,081,660 ) - Segment revenue 130,212,726 27,275,730 163,116,554 16,360,757 - 336,965,767 Interest income 32,499 41,405 130,659 37,297 (11,793 ) 230,067 Interest expense (1,727,127 ) (5,980 ) (44,433 ) (451,790 ) 11,793 (2,217,537 ) Depreciation and amortization (18,706,891 ) (6,566,936 ) (2,759,298 ) (1,437,312 ) - (29,470,437 ) Share of the profit of associates and joint ventures 1,513,394 (9,484 ) - - - 1,503,910 Impairment loss (974,095 ) (4,136 ) (1,886 ) - - (980,117 ) Segment profit before income tax 13,921,640 7,226,531 4,626,263 2,194,271 - 27,968,705 Expenditures for segment assets 17,561,135 8,247,003 906,042 966,682 - 27,680,862 December 31, 2016 Investments accounted for using the equity method 49,597,195 227,495 - - - 49,824,690 For the year ended December 31, 2017 Revenue from external customers 126,225,119 26,157,277 133,948,016 4,110,796 - 290,441,208 Inter-segment revenue (Note 1) 4,911,026 184,707 47,119,404 8,383,640 (60,598,777 ) - Segment revenue 131,136,145 26,341,984 181,067,420 12,494,436 - 351,039,985 Interest income 43,744 48,532 269,640 214,265 (269,310 ) 306,871 Interest expense (1,969,562 ) (11,920 ) - (62,714 ) 269,310 (1,774,886 ) Depreciation and amortization (19,105,457 ) (6,476,743 ) (2,133,253 ) (1,489,731 ) - (29,205,184 ) Share of the profit or loss of associates and joint ventures 568,291 (42,509 ) - - - 525,782 Impairment loss (218,214 ) (72,798 ) - (473,869 ) - (764,881 ) Segment profit before income tax 12,065,304 6,904,067 6,883,327 5,167,965 - 31,020,663 Expenditures for segment assets 17,769,612 4,507,097 850,235 550,738 - 23,677,682 December 31, 2017 Investments accounted for using the equity method 48,566,333 187,418 - - - 48,753,751 Adjustments Packaging Testing EMS Others and Eliminations Total NT$ NT$ NT$ NT$ NT$ NT$ For the year ended December 31, 2018 Revenue from external customers $ 178,308,222 $ 35,903,202 $ 151,890,384 $ 4,990,613 $ - $ 371,092,421 Inter-segment revenues (Note 1) 3,531,431 212,310 58,836,465 7,637,053 (70,217,259 ) - Segment revenues 181,839,653 36,115,512 210,726,849 12,627,666 - 441,309,680 Interest income 166,761 55,108 354,343 352,232 (462,233 ) 466,211 Interest expense (3,647,601 ) (101,338 ) - (249,180 ) 462,233 (3,535,886 ) Depreciation and amortization (29,491,977 ) (9,560,610 ) (2,065,590 ) (1,570,726 ) - (42,688,903 ) Share of the profit or loss of associates and joint ventures (456,846 ) (23,398 ) - - - (480,244 ) Impairment loss (654,081 ) - - - - (654,081 ) Segment profit before income tax 17,866,431 7,952,484 6,225,984 (107,221 ) - 31,937,678 Expenditures for segment assets 22,787,190 12,991,023 2,529,771 784,254 - 39,092,238 December 31, 2018 Investments accounted for using the equity method 9,152,290 160,018 - - - 9,312,308 Contract assets 3,488,372 1,000,128 - - - 4,488,500 Adjustments Packaging Testing EMS Others and Eliminations Total US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) For the year ended December 31, 2018 Revenue from external customers $ 5,825,163 $ 1,172,924 $ 4,962,116 $ 163,039 $ - $ 12,123,242 Inter-segment revenues (Note 1) 115,369 6,936 1,922,132 249,495 (2,293,932 ) - Segment revenues 5,940,532 1,179,860 6,884,248 412,534 - 14,417,174 Interest income 5,448 1,801 11,576 11,507 (15,101 ) 15,231 Interest expense (119,164 ) (3,311 ) - (8,140 ) 15,101 (115,514 ) Depreciation and amortization (963,475 ) (312,336 ) (67,481 ) (51,315 ) - (1,394,607 ) Share of the profit or loss of associates and joint ventures (14,925 ) (764 ) - - - (15,689 ) Impairment loss (21,368 ) - - - - (21,368 ) Segment profit before income tax 583,680 259,800 203,397 (3,503 ) - 1,043,374 Expenditures for segment assets 744,436 424,404 82,645 25,621 - 1,277,106 December 31, 2018 Investments accounted for using the equity method 298,996 5,228 - - - 304,224 Contract assets 113,962 32,673 - - - 146,635 Note 1: Inter-segment revenues were eliminated upon consolidation. Note 2: Refer to the table above for information about disaggregation of revenue. b. Revenue from major products and services For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Packaging service $ 125,282,829 $ 126,225,119 $ 178,308,222 $ 5,825,163 Testing service 27,031,750 26,157,277 35,903,202 1,172,924 Electronic components manufacturing service 115,395,130 133,948,016 151,890,384 4,962,116 Others 7,174,398 4,110,796 4,990,613 163,039 $ 274,884,107 $ 290,441,208 $ 371,092,421 $ 12,123,242 c. Geographical information Geographical information about revenue from external customers and noncurrent assets are reported based on the country where the external customers are headquartered and noncurrent assets are located, respectively. 1) Net revenues from external customers For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) United States $ 180,745,837 $ 196,462,345 $ 230,791,164 $ 7,539,731 Taiwan 38,868,679 35,413,647 45,630,792 1,490,715 Asia 29,896,304 30,201,332 56,031,108 1,830,484 Europe 23,275,732 26,445,240 36,844,258 1,203,668 Others 2,097,555 1,918,644 1,795,099 58,644 $ 274,884,107 $ 290,441,208 $ 371,092,421 $ 12,123,242 2) Non-current assets, excluding financial instruments, post-employment benefit assets and deferred tax assets December 31 2017 2018 NT$ NT$ US$ (Note 4) Taiwan $ 93,350,839 $ 229,944,505 $ 7,512,071 China 45,376,164 59,058,239 1,929,377 Others 25,025,498 25,686,256 839,146 $ 163,752,501 $ 314,689,000 $ 10,280,594 d. Major customers Except one customer from which the operating revenues generated from packaging and EMS segments was NT$66,554,659 thousand, NT$83,873,393 thousand and NT$92,117,839 thousand (US$3,009,403 thousand) in 2016, 2017 and 2018, respectively, the Group did not have other single customer to which the operating revenues exceeded 10% of operating revenues for the years ended December 31, 2016, 2017 and 2018.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Statement of Compliance	a. Statement of compliance The consolidated financial statements have been prepared in accordance with IFRSs as issued by the IASB.
Basis of Preparation	b. Basis of preparation As disclosed in Note 1, the share exchange between the Company and ASE was an organization restructure under common control that the Company was essentially the continuation of ASE. The related assets and liabilities in the Company’s consolidated financial statements, before the date of incorporation, were recognized based on the carrying amounts of those in ASE’s consolidated financial statements. The consolidated financial statements of the Company for prior periods are prepared under the assumption that the Company owned 100% shareholdings of ASE at the very beginning. The consolidated financial statements have been prepared on the historical cost basis except for financial instruments which are measured at fair value and net defined benefit liabilities which are measured at the present value of the defined benefit obligation less the fair value of plan assets. The fair value measurements, which are grouped into Levels 1 to 3 based on the degree to which the fair value measurement inputs are observable and based on the significance of the inputs to the fair value measurement in its entirety, are described as follows: 1) Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities; 2) Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for an asset or a liability, either directly (i.e. as prices) or indirectly (i.e. derived from prices); and 3) Level 3 inputs are unobservable inputs for an asset or a liability.
Classification of Current and Non-current Assets and Liabilities	c. Classification of current and non-current assets and liabilities Current assets include cash and cash equivalents and those assets held primarily for trading purposes or expected to be realized within twelve months after the balance sheet date, unless the asset is to be used for an exchange or to settle a liability, or otherwise remains restricted, at more than twelve months after the balance sheet date. Current liabilities are obligations incurred for trading purposes or to be settled within twelve months after the balance sheet date (even if an agreement to refinance, or to reschedule payments, on a long-term basis is completed after the balance sheet date and before the consolidated financial statements are authorized for issue) and liabilities that do not have an unconditional right to defer settlement for at least 12 months after the balance sheet date (terms of a liability that could, at the option of the counterparty, result in its settlement by the issue of equity instruments do not affect its classification). Assets and liabilities that are not classified as current are classified as non-current. The Group engages in the construction business which has an operating cycle of over one year. The normal operating cycle applies when considering the classification of the Group’s construction-related assets and liabilities.
Basis of Consolidation	d. Basis of consolidation 1) Principles for preparing consolidated financial statements The Company became the ultimate parent company of the Group after completing the share exchange with ASE on April 30, 2018. In addition, the Company obtained control over SPIL on April 30, 2018 and, therefore, included SPIL’s subsidiaries in the Group’s consolidated financial statements from the same date. The consolidated financial statements incorporate the financial statements of the Company and the entities controlled by the Company (i.e. its subsidiaries, including structured entities). Income and expenses of subsidiaries acquired or disposed of during the period are included in the consolidated statement of profit or loss and other comprehensive income from the effective dates of acquisitions up to the effective dates of disposals, as appropriate. When necessary, adjustments are made to the financial statements of subsidiaries to bring their accounting policies into line with those used by the Company. All intra-group transactions, balances, income and expenses are eliminated in full upon consolidation. Total comprehensive income of subsidiaries is attributed to the owners of the Company and to the non-controlling interests even if this results in the non-controlling interests having a deficit balance. Changes in the Group’s ownership interests in subsidiaries that do not result in the Group losing control over the subsidiaries are accounted for as equity transactions. The carrying amounts of the interests of the Group and the non-controlling interests are adjusted to reflect the changes in their relative interests in the subsidiaries. Any difference between the amount by which the non-controlling interests are adjusted and the fair value of the consideration paid or received is recognized directly in equity and attributed to the owners of the Company. When the Group loses control of a subsidiary, a gain or loss is recognized in profit or loss and is calculated as the difference between (i) the aggregate of the fair value of the consideration received and any investment retained in the former subsidiary at its fair value at the date when control is lost and (ii) the assets (including any goodwill) and liabilities and any non-controlling interests of the former subsidiary at their carrying amounts at the date when control is lost. The Group accounts for all amounts recognized in other comprehensive income in relation to that subsidiary on the same basis as would be required had the Group directly disposed of the related assets or liabilities. 2) Subsidiaries included in consolidated financial statements were as follows: Establishment and Percentage of Ownership (%) December 31 Name of Investee Main Businesses Operating Location 2017 2018 ASE Engaged in the packaging and testing of semiconductors Kaohsiung, R.O.C. 100.0 100.0 A.S.E. Holding Limited Holding company Bermuda 100.0 100.0 J & R Holding Limited (“J&R Holding”) Holding company Bermuda 100.0 100.0 Innosource Limited Holding company British Virgin Islands 100.0 100.0 Omniquest Industrial Limited Holding company British Virgin Islands 100.0 100.0 ASE Marketing & Service Japan Co., Ltd. Engaged in marketing and sales services Japan 100.0 100.0 ASE Test, Inc. Engaged in the testing of semiconductors Kaohsiung, R.O.C. 100.0 100.0 Luchu Development Corporation Engaged in the development of real estate properties Taipei, R.O.C. 86.1 86.1 TLJ Intertech Inc. (“TLJ”) Engaged in information software services Taipei, R.O.C. 60.0 60.0 MingFung Information Service Corp., Ltd. Engaged in information software services, and was established in May 2018. Taipei, R.O.C. - 100.0 Alto Enterprises Limited Holding company British Virgin Islands 100.0 100.0 Super Zone Holdings Limited Holding company Hong Kong 100.0 100.0 ASE (Kun Shan) Inc. Engaged in the packaging and testing of semiconductors Kun Shan, China 100.0 100.0 ASE Investment (Kun Shan) Limited Holding company Kun Shan, China 100.0 100.0 Advanced Semiconductor Engineering (China) Ltd. Will engage in the packaging and testing of semiconductors Shanghai, China 100.0 100.0 ASE Investment (Labuan) Inc. Holding company Malaysia 100.0 100.0 ASE Test Limited (“ASE Test”) Holding company Singapore 100.0 100.0 ASE (Korea) Inc. (“ASE Korea”) Engaged in the packaging and testing of semiconductors Korea 100.0 100.0 J&R Industrial Inc. Engaged in leasing equipment and investing activity Kaohsiung, R.O.C. 100.0 100.0 ASE Japan Co., Ltd. (“ASE Japan”) Engaged in the packaging and testing of semiconductors Japan 100.0 100.0 ASE (U.S.) Inc. After-sales service and sales support U.S.A. 100.0 100.0 Global Advanced Packaging Technology Limited Holding company British Cayman Islands 100.0 100.0 ASE WeiHai Inc. Engaged in the packaging and testing of semiconductors Shandong, China 100.0 100.0 Establishment and Percentage of Ownership (%) December 31 Name of Investee Main Businesses Operating Location 2017 2018 Suzhou ASEN Semiconductors Co., Ltd. (“ASEN”) Engaged in the packaging and testing of semiconductors Suzhou, China 60.0 70.0 Anstock Limited Engaged in financing activity British Cayman Islands 100.0 100.0 Anstock II Limited Engaged in financing activity British Cayman Islands 100.0 100.0 ASE (Shanghai) Inc. Engaged in the production of substrates Shanghai, China 100.0 100.0 ASE Corporation Holding company British Cayman Islands 100.0 100.0 ASE Mauritius Inc. Holding company Mauritius 100.0 100.0 ASE Labuan Inc. Holding company Malaysia 100.0 100.0 Shanghai Ding Hui Real Estate Development Co., Ltd. Engaged in the development, construction and sale of real estate properties Shanghai, China 100.0 100.0 Shanghai Ding Qi Property Management Co., Ltd. Engaged in the management of real estate properties Shanghai, China 100.0 100.0 Advanced Semiconductor Engineering (HK) Limited Engaged in the trading of substrates Hong Kong 100.0 100.0 Shanghai Ding Wei Real Estate Development Co., Ltd. Engaged in the development, construction and leasing of real estate properties Shanghai, China 100.0 100.0 Shanghai Ding Yu Real Estate Development Co., Ltd. Engaged in the development, construction and leasing of real estate properties Shanghai, China 100.0 100.0 Shanghai Ding Fan Department Store Co., Ltd. Engaged in department store business Shanghai, China 100.0 100.0 Kun Shan Ding Hong Real Estate Development Co., Ltd. Engaged in the development, construction and leasing of real estate properties Kun Shan, China 100.0 100.0 Shanghai Ding Xu Property Management Co., Ltd. Engaged in the management of real estate properties Shanghai, China 100.0 100.0 ASE Electronics Inc. Engaged in the production of substrates Kaohsiung, R.O.C. 100.0 100.0 ASE Test Holdings, Ltd. Holding company British Cayman Islands 100.0 100.0 ASE Holdings (Singapore) Pte. Ltd. Holding company Singapore 100.0 100.0 ASE Singapore Pte. Ltd. Engaged in the packaging and testing of semiconductors Singapore 100.0 100.0 ISE Labs, Inc. Engaged in the testing of semiconductors U.S.A. 100.0 100.0 ASE Electronics (M) Sdn. Bhd. Engaged in the packaging and testing of semiconductors Malaysia 100.0 100.0 ASE Assembly & Test (Shanghai) Limited Engaged in the packaging and testing of semiconductors Shanghai, China 100.0 100.0 Establishment and Percentage of Ownership (%) December 31 Name of Investee Main Businesses Operating Location 2017 2018 ASE Trading (Shanghai) Ltd. Liquidated in December 2018 Shanghai, China 100.0 - ISE Labs, China, Ltd. Engaged in the testing of semiconductors, and was established in October 2018 Shanghai, China - 100.0 Wuxi Tongzhi Microelectronics Co., Ltd. Engaged in the packaging and testing of semiconductors Wuxi, China 100.0 100.0 USI Global Engaged in investing activities, and was established in November 2018 and then dissolved in January 2019 Nantou, R.O.C. - 100.0 USIINC Engaged in investing activity Nantou, R.O.C. 99.2 100.0 Huntington Holdings International Co., Ltd. Holding company British Virgin Islands 99.2 100.0 Unitech Holdings International Co., Ltd. (“UHI”) Holding company British Virgin Islands 99.2 100.0 Real Tech Holdings Limited Holding company British Virgin Islands 99.2 100.0 Universal ABIT Holding Co., Ltd. In the process of liquidation British Cayman Islands 99.2 100.0 Rising Capital Investment Limited Holding company British Virgin Islands 99.2 100.0 Rise Accord Limited Holding company British Virgin Islands 99.2 100.0 Universal Scientific Industrial (Kunshan) Co., Ltd. Engaged in the manufacturing and sale of computer assistance system and related peripherals Kun Shan, China 99.2 100.0 USI Enterprise Limited (“USIE”) Engaged in the services of investment advisory and warehousing management Hong Kong 96.9 95.4 Universal Scientific Industrial (Shanghai) Co., Ltd. (“USISH”) Engaged in the designing, manufacturing and sale of electronic components Shanghai, China 75.8 74.6 Universal Global Technology Co., Limited Holding company Hong Kong 75.8 74.6 Universal Global Technology (Kunshan) Co., Ltd. Engaged in the designing and manufacturing of electronic components Kun Shan, China 75.8 74.6 Universal Global Technology (Shanghai) Co., Ltd. Engaged in the processing and sales of computer and communication peripherals as well as business in import and export of goods and technology Shanghai, China 75.8 74.6 Universal Global Electronics (Shanghai) Co., Ltd. Engaged in the sale of electronic components and telecommunications equipment Shanghai, China 75.8 74.6 Establishment and Percentage of Ownership (%) December 31 Name of Investee Main Businesses Operating Location 2017 2018 USI America Inc. Engaged in the manufacturing and processing of motherboards and wireless network communication and provision of related technical service U.S.A. 75.8 74.6 Universal Global Industrial Co., Limited Engaged in manufacturing, trading and investing activity Hong Kong 75.8 74.6 Universal Global Scientific Industrial Co., Ltd. (“UGTW”) Engaged in the manufacturing of components of telecomm and cars and provision of related R&D services Nantou, R.O.C. 75.8 74.6 Universal Scientific Industrial De Mexico S.A. De C.V. Engaged in the assembling of motherboards and computer components Mexico 75.8 74.6 USI Japan Co., Ltd. Engaged in the manufacturing and sale of computer peripherals, integrated chip and other related accessories Japan 75.8 74.6 USI Electronics (Shenzhen) Co., Ltd. Engaged in the design, manufacturing and sale of motherboards and computer peripherals Shenzhen, China 75.8 74.6 Universal Global Electronics Co., Ltd. Engaged in accepting and outsourcing orders as well as sales of electronic components and service of technical advisory, and was established in February 2018 Hong Kong - 74.6 Universal Scientific Industrial Co., Ltd. (“USI”) Engaged in the manufacturing, processing and sale of computers, computer peripherals and related accessories Nantou, R.O.C. 75.5 74.4 SPIL Engaged in the assembly, testing and turnkey services of integrated circuits Taichung, R.O.C. - 100.0 SPIL (B.V.I.) Holding Limited Engaged in investing activities British Virgin Islands - 100.0 Siliconware Investment Co., Ltd. Engaged in investing activities Taipei, R.O.C. - 100.0 Siliconware USA, Inc. Engaged in marketing activities U.S.A. - 100.0 Establishment and Percentage of Ownership (%) December 31 Name of Investee Main Businesses Operating Location 2017 2018 SPIL (Cayman) Holding Limited Engaged in investing activities British Cayman Islands - 100.0 Siliconware Technology (Suzhou) Limited Engaged in the packaging and testing of semiconductors Suzhou, China - 70.0 Siliconware Electronics (Fujian) Co., Limited Engaged in the packaging and testing of semiconductors Fujian, China - 100.0
Business Combinations	e. Business combinations Acquisitions of businesses are accounted for using the acquisition method. Acquisition-related costs are generally recognized in profit or loss as they are incurred. Goodwill is measured as the excess of the sum of the consideration transferred, the amount of any non-controlling interests in the acquiree, and the fair value of the acquirer’s previously held equity interest in the acquiree (if any) over the net of the acquisition-date amounts of the identifiable assets acquired and the liabilities assumed. If, after re-assessment, the net of the acquisition-date amounts of the identifiable assets acquired and liabilities assumed exceeds the sum of the consideration transferred, the amount of any non-controlling interests in the acquiree and the fair value of the acquirer’s previously held interest in the acquiree (if any), the excess is recognized immediately in profit or loss as a bargain purchase gain. When a business combination is achieved in stages, the Group’s previously held equity interest in the acquiree is remeasured to its acquisition-date fair value and the resulting gain or loss, if any, is recognized in profit or loss or other comprehensive income. Amounts arising from interests in the acquiree prior to the acquisition date that have previously been recognized in other comprehensive income are recognized on the same basis as would be required if that interest were directly disposed of by the Group. If the initial accounting for a business combination is incomplete by the end of the reporting period in which the combination occurs, the Group reports provisional amounts for the items for which the accounting is incomplete. Those provisional amounts are adjusted retrospectively during the measurement period, or additional assets or liabilities are recognized, to reflect new information obtained about facts and circumstances that existed at the acquisition date that, if known, would have affected the amounts recognized at that date. Business combination involving entities under common control is not accounted for by acquisition method but accounted for at the carrying amounts of the entities.
Foreign Currencies	f. Foreign currencies In preparing the financial statements of each individual group entity, transactions in currencies other than the entity’s functional currency (i.e. foreign currencies) are recognized at the rates of exchange prevailing at the dates of the transactions. At each balance sheet date, monetary items denominated in foreign currencies are retranslated at the rates prevailing at that date. Exchange differences on monetary items arising from settlement or translation are recognized in profit or loss in the period in which they arise except for exchange differences on transactions entered into in order to hedge certain foreign currency risks. Non-monetary items measured at fair value that are denominated in foreign currencies are retranslated at the rates prevailing at the date when the fair value was determined. Exchange differences arising from the retranslation of non-monetary items are included in profit or loss for the period except for exchange differences arising from the retranslation of non-monetary items in respect of which gains and losses are recognized directly in other comprehensive income, in which cases, the exchange differences are also recognized directly in other comprehensive income. Non-monetary items that are measured at historical cost in a foreign currency are translated using the exchange rate at the date of the transaction, and are not retranslated. For the purposes of presenting the consolidated financial statements, the assets and liabilities of the Group’s foreign operations (including subsidiaries, associates and joint ventures in other countries that use currencies which are different from the currency of the Company) are translated into the New Taiwan dollars using exchange rates prevailing at each balance sheet date. Income and expense items are translated at the average exchange rates for the period. The resulting currency translation differences are recognized in other comprehensive income and accumulated in equity attributed to the owners of the Company and non-controlling interests as appropriate. On the disposal of the Group’s entire interest in a foreign operation, or a disposal involving the loss of control over a subsidiary that includes a foreign operation, or a partial disposal of an interest in a joint arrangement or an associate that includes a foreign operation of which the retained interest becomes a financial asset, all of the exchange differences accumulated in equity in respect of that operation attributable to the owners of the Company are reclassified to profit or loss. In relation to a partial disposal of a subsidiary that does not result in the Group losing control over the subsidiary, the proportionate share of accumulated exchange differences is re-attributed to the non-controlling interests of the subsidiary and is not recognized in profit or loss. For all other partial disposals, the proportionate share of the accumulated exchange differences recognized in other comprehensive income is reclassified to profit or loss.
Inventories and Inventories Related to Real Estate Business	g. Inventories and inventories related to real estate business Inventories, including raw materials (materials received from customers for processing, mainly semiconductor wafers, are excluded from inventories as title and risk of loss remain with the customers), supplies, work in process, finished goods, and materials and supplies in transit are stated at the lower of cost or net realizable value. Inventory write-downs are made by item, except for those that may be appropriate to group items of similar or related inventories. Net realizable value is the estimated selling prices of inventories less all estimated costs of completion and estimated costs necessary to make the sale. Raw materials and supplies are recorded at moving average cost while work in process and finished goods are recorded at standard cost. Inventories related to real estate business include land and buildings held for sale, land held for construction and construction in progress. Land held for development is recorded as land held for construction upon obtaining the title of ownership. Prior to the completion, the borrowing costs directly attributable to construction in progress are capitalized as part of the cost of the asset. Construction in progress is transferred to land and buildings held for sale upon completion. Land and buildings held for sale, construction in progress and land held for construction are stated at the lower of cost or net realizable value and related write-downs are made by item. The amounts received in advance for real estate properties are first recorded as advance receipts and then recognized as revenue when the construction is completed and the title and significant risk of the real estate properties are transferred to customers. Cost of sales of land and buildings held for sale are recognized based on the ratio of property sold to the total property developed.
Investments in associates and joint ventures	h. Investments in associates and joint ventures An associate is an entity over which the Group has significant influence and that is neither a subsidiary nor an interest in a joint venture. Joint venture is a joint arrangement whereby the Group and other parties that have joint control of the arrangement have rights to the net assets of the arrangement. Under the equity method, investments in an associate and a joint venture are initially recognized at cost and adjusted thereafter to recognize the Group’s share of the profit or loss and other comprehensive income of the associate and joint venture. The Group also recognizes the changes in the Group’s share of equity of associates and joint venture. Any excess of the cost of acquisition over the Group’s share of the net fair value of the identifiable assets and liabilities of an associate or a joint venture at the date of acquisition is recognized as goodwill, which is included within the carrying amount of the investment and is not amortized. Any excess of the Group’s share of the net fair value of the identifiable assets and liabilities over the cost of acquisition after reassessment is recognized immediately in profit or loss. When the Group subscribes for additional new shares of an associate and joint venture at a percentage different from its existing ownership percentage, the resulting carrying amount of the investment differs from the amount of the Group’s proportionate interest in the associate and joint venture. The Group records such a difference as an adjustment to investments with the corresponding amount charged or credited to capital surplus - changes in capital surplus from investments in associates and joint ventures accounted for using the equity method. If the Group’s ownership interest is reduced due to its additional subscription of the new shares of the associate and joint venture, the proportionate amount of the gains or losses previously recognized in other comprehensive income in relation to that associate and joint venture is reclassified to profit or loss on the same basis as would be required had the investee directly disposed of the related assets or liabilities. When the adjustment should be debited to capital surplus, but the capital surplus recognized from investments accounted for using the equity method is insufficient, the shortage is debited to retained earnings. When the Group’s share of losses of an associate and a joint venture equals or exceeds its interest in that associate and joint venture (which includes any carrying amount of the investment accounted for using the equity method and long-term interests that, in substance, form part of the Group’s net investment in the associate and joint venture), the Group discontinues recognizing its share of further losses. Additional losses and liabilities are recognized only to the extent that the Group has incurred legal obligations or constructive obligations, or made payments on behalf of that associate and joint venture. The entire carrying amount of an investment (including goodwill) is tested for impairment as a single asset by comparing its recoverable amount with its carrying amount. Any impairment loss recognized is not allocated to any asset, including goodwill, that forms part of the carrying amount of the investment. Any reversal of that impairment loss is recognized to the extent that the recoverable amount of the investment subsequently increases. The Group discontinues the use of the equity method from the date on which its investment ceases to be an associate and a joint venture. Any retained investment is measured at fair value at that date, and the fair value is regarded as the investment’s fair value on initial recognition as a financial asset. The difference between the previous carrying amount of the associate and the joint venture attributable to the retained interest and its fair value is included in the determination of the gain or loss on disposal of the associate and the joint venture. The Group accounts for all amounts previously recognized in other comprehensive income in relation to that associate and joint venture on the same basis as would be required had that associate directly disposed of the related assets or liabilities. If an investment in an associate becomes an investment in a joint venture or an investment in a joint venture becomes an investment in an associate, the Group continues to apply the equity method and does not remeasure the retained interest. When a group entity transacts with its associate and joint venture, profits and losses resulting from the transactions with the associate and joint venture are recognized in the Group’ consolidated financial statements only to the extent that interests in the associate and the joint venture are not related to the Group.
Property, Plant and Equipment	i. Property, plant and equipment Except for land which is stated at cost, property, plant and equipment (including assets held under finance leases) are stated at cost less accumulated depreciation and accumulated impairment. Properties in the course of construction are carried at cost, less any recognized impairment loss. Cost includes professional fees and borrowing costs eligible for capitalization. Such assets are depreciated and classified to the appropriate categories of property, plant and equipment when completed and ready for their intended use. Freehold land is not depreciated. Depreciation of property, plant and equipment is recognized using the straight-line method. Each significant part is depreciated separately. If the lease term is shorter than the assets’ useful lives, such assets are depreciated over the lease term. The estimated useful lives, residual values and depreciation method are reviewed at each balance sheet date, with the effect of any changes in estimate accounted for on a prospective basis. On derecognition of an item of property, plant and equipment, the difference between the sales proceeds and the carrying amount of the asset is recognized in profit or loss.
Investment Properties	j. Investment properties Investment properties are properties held to earn rentals and/or for capital appreciation (including property under construction for such purposes). Investment properties also include land held for a currently undetermined future use. Investment properties are measured initially at cost, including transaction costs. Subsequent to initial recognition, investment properties are measured at cost less accumulated depreciation and accumulated impairment loss. Depreciation is recognized using the straight-line method. Investment properties under construction are stated at cost less accumulated depreciation and accumulated impairment loss. Cost includes professional fees and borrowing costs eligible for capitalization. Depreciation of these assets commences when the assets are ready for their intended use. For a transfer from property, plant and equipment to investment properties, the property’s deemed cost for subsequent accounting is its carrying amount at the end of owner-occupation. For a transfer from inventories to investment properties, the property’s deemed cost for subsequent accounting is its carrying amount at inception of an operating lease. On derecognition of an investment property, the difference between the net disposal proceeds and the carrying amount of the asset is included in profit or loss.
Goodwill	k. Goodwill Goodwill arising from an acquisition of a business is carried at cost as established at the date of acquisition of the business less accumulated impairment loss. For the purposes of impairment testing, goodwill is allocated to each of the Group’s cash-generating units or groups of cash-generating units (referred to as “cash-generating units”) that is expected to benefit from the synergies of the combination. A cash-generating unit to which goodwill has been allocated is tested for impairment annually, or more frequently when there is an indication that the unit may be impaired, by comparing its carrying amount, including the attributed goodwill, with its recoverable amount. However, if the goodwill allocated to a cash-generating unit was acquired in a business combination during the current annual period, that unit shall be tested for impairment before the end of the current annual period. If the recoverable amount of the cash-generating unit is less than its carrying amount, the impairment loss is allocated first to reduce the carrying amount of any goodwill allocated to the unit and then pro rata to the other assets of the unit based on the carrying amount of each asset in the unit. Any impairment loss is recognized directly in profit or loss. An impairment loss recognized for goodwill is not reversed in subsequent periods.
Other Intangible Assets	l. Other intangible assets Other intangible assets with finite useful lives acquired separately are initially measured at cost and subsequently measured at cost less accumulated amortization and accumulated impairment loss. Other intangible assets are amortized using the straight-line method over their estimated useful lives. The estimated useful lives, residual values, and amortization methods are reviewed at each balance sheet date, with the effect of any changes in estimate being accounted for on a prospective basis. Other intangible assets acquired in a business combination and recognized separately from goodwill are initially recognized at their fair value at the acquisition date which is regarded as their cost. Subsequent to initial recognition, they are measured on the same basis as intangible assets that are acquired separately. On derecognition of an intangible asset, the difference between the net disposal proceeds and the carrying amount of the asset are recognized in profit or loss.
Impairment of Tangible and Intangible Assets Other than Goodwill	m. Impairment of tangible and intangible assets other than goodwill At each balance sheet date, the Group reviews the carrying amounts of its tangible and intangible assets, excluding goodwill, to determine whether there is any indication that those assets have suffered an impairment loss. If any such indication exists, the recoverable amount of the asset is estimated in order to determine the extent of the impairment loss. When it is not possible to estimate the recoverable amount of an individual asset, the Group estimates the recoverable amount of the cash-generating unit to which the asset belongs. Corporate assets are allocated to the individual cash-generating units on a reasonable and consistent basis of allocation. The recoverable amount is the higher of fair value less costs to sell and value in use. If the recoverable amount of an asset or cash-generating unit is estimated to be less than its carrying amount, the carrying amount of the asset or cash-generating unit is reduced to its recoverable amount, with the resulting impairment loss recognized in profit or loss. When an impairment loss is subsequently reversed, the carrying amount of the asset or cash-generating unit is increased to the revised estimate of its recoverable amount, but only to the extent of the carrying amount that would have been determined had no impairment loss been recognized for the asset or cash-generating unit in prior years. A reversal of an impairment loss is recognized immediately in profit or loss.
Financial Instruments	n. Financial instruments Financial assets and financial liabilities are recognized when a group entity becomes a party to the contractual provisions of the instruments. Financial assets and financial liabilities are initially measured at fair value. Transaction costs that are directly attributable to the acquisition or issue of financial assets and financial liabilities (other than financial assets and financial liabilities at FVTPL) are added to or deducted from the fair value of the financial assets or financial liabilities, as appropriate, on initial recognition. Transaction costs directly attributable to the acquisition of financial assets or financial liabilities at fair value through profit or loss are recognized immediately in profit or loss. 1) Financial assets All regular way purchases or sales of financial assets are recognized and derecognized on a settlement date basis. a) Measurement category 2018 Financial assets held by the Group are classified into the following categories: financial assets at FVTPL, financial assets at amortized cost, and investments in debt instruments and equity instruments at FVTOCI. i. Financial asset at FVTPL Financial asset is classified as at FVTPL when the financial asset is mandatorily classified or it is designated as at FVTPL. The Group’s financial assets mandatorily classified as at FVTPL include investments in equity instruments which are not designated as at FVTOCI and debt instruments that do not meet the amortized cost criteria or the FVTOCI criteria. A financial asset may be designated as at FVTPL upon initial recognition if such designation eliminates or significantly reduces a measurement or recognition inconsistency that would otherwise arise. Financial assets at FVTPL are subsequently measured at fair value, with any gains or losses arising on remeasurement recognized in profit or loss. The net gain or loss recognized in profit or loss incorporates any dividend or interest earned on the financial asset. Fair value is determined in the manner described in Note 36. ii. Financial assets at amortized cost Financial assets that meet the following conditions are subsequently measured at amortized cost: i) The financial asset is held within a business model whose objective is to hold financial assets in order to collect contractual cash flows; and ii) The contractual terms of the financial asset give rise on specified dates to cash flows that are solely payments of principal and interest on the principal amount outstanding. Subsequent to initial recognition, financial assets at amortized cost, including cash and cash equivalents, trade receivables at amortized cost, other receivables and other financial assets, are measured at amortized cost, which equals to gross carrying amount determined using the effective interest method less any impairment loss. Exchange differences are recognized in profit or loss. Interest income is calculated by applying the effective interest rate to the gross carrying amount of a financial asset, except for: i) Purchased or originated credit-impaired financial assets, for which interest income is calculated by applying the credit-adjusted effective interest rate to the amortized cost of the financial asset; and ii) Financial assets that are not credit-impaired on purchase or origination but have subsequently become credit-impaired, for which interest income is calculated by applying the effective interest rate to the amortized cost of such financial assets in subsequent reporting periods. Cash equivalents include time deposits with original maturities within 3 months from the date of acquisition, which are highly liquid, readily convertible to a known amount of cash and are subject to an insignificant risk of changes in value. These cash equivalents are held for the purpose of meeting short-term cash commitments. iii. Investments in debt instruments at FVTOCI For the Group’s debt instruments that meet the following conditions are subsequently measured at FVTOCI: i) the debt instrument is held within a business model whose objective is achieved by both the collecting of contractual cash flows and the selling of the financial assets; and ii) the contractual terms of the debt instrument give rise on specified dates to cash flows that are solely payments of principal and interest on the principal amount outstanding. Investments in debt instruments at FVTOCI are subsequently measured at fair value. Changes in the carrying amounts of these debt instruments relating to changes in foreign currency exchange rates, interest income calculated using the effective interest method and impairment losses or reversals are recognized in profit or loss. Other changes in the carrying amount of these debt instruments are recognized in other comprehensive income and will be reclassified to profit or loss when the investment is disposed of. iv. Investments in equity instruments at FVTOCI On initial recognition, the Group make an irrevocable election to designate investments in equity instruments as at FVTOCI. Designation at FVTOCI is not permitted if the equity investment is held for trading or if it is contingent consideration recognized by an acquirer in a business combination. Investments in equity instruments at FVTOCI are subsequently measured at fair value with gains and losses arising from changes in fair value recognized in other comprehensive income and accumulated in other equity. The cumulative gain or loss will not be reclassified to profit or loss on disposal of the equity investments, instead, they will be transferred to retained earnings. Dividends on these investments in equity instruments are recognized in profit or loss when the Group’s right to receive the dividends is established, unless the dividends clearly represent a recovery of part of the cost of the investment. Prior to 2018 The classification of financial assets held by ASE and its subsidiaries includes financial assets at FVTPL, available-for-sale financial assets, and loans and receivables. i. Financial assets at FVTPL Financial assets are classified as at FVTPL when the financial assets are either held for trading or they are designated as at FVTPL. A financial asset other than a financial asset held for trading may be designated as at FVTPL upon initial recognition if: i) Such designation eliminates or significantly reduces a measurement or recognition inconsistency that would otherwise arise; or ii) The financial asset forms part of a group of financial assets or financial liabilities or both, which is managed and has performance evaluated on a fair value basis in accordance with ASE and its subsidiaries’ documented risk management or investment strategy, and information about the grouping is provided internally on that basis; or iii) The contract contains one or more embedded derivatives so that the entire hybrid (combined) contract can be designated as at FVTPL. Financial assets at FVTPL are stated at fair value with any gains or losses arising on remeasurement recognized in profit or loss. The net gain or loss recognized in profit or loss incorporates any dividend or interest earned on the financial asset. Fair value is determined in the manner described in Note 36. ii. Available-for-sale financial assets Available-for-sale financial assets are non-derivatives that are either designated as available-for-sale or are not classified as (1) loans and receivables, (2) held-to-maturity investments or (3) financial assets at fair value through profit or loss. Available-for-sale financial assets are stated at fair value at each balance sheet date. Changes in the carrying amount of available-for-sale monetary financial assets relating to changes in foreign currency rates, interest income calculated using the effective interest method and dividends on available-for-sale equity investments are recognized in profit or loss. Other changes in the carrying amount of available-for-sale financial assets are recognized in other comprehensive income and accumulated under the heading of unrealized gain (loss) on available-for-sale financial assets. When the investment is disposed of or is determined to be impaired, the cumulative gain or loss previously accumulated in the unrealized gain (loss) on available-for-sale financial assets is reclassified to profit or loss. Dividends on available-for-sale equity instruments are recognized in profit or loss when ASE and its subsidiaries’s right to receive the dividends is established. iii. Loans and receivables Loans and receivables including cash and cash equivalents, trade receivables, other receivables and other financial assets are measured at amortized cost using the effective interest method, less any impairment. Interest income is recognized by applying the effective interest rate, except for short-term receivables when the effect of discounting is immaterial. Cash equivalents are short-term, highly liquid investments that are readily convertible to known amounts of cash and which are subject to an insignificant risk of change in value. b) Impairment of financial assets and contract assets 2018 At each balance sheet date, the Group recognizes a loss allowance for expected credit losses on financial assets at amortized cost (including trade receivables), investments in debt instruments that are measured at FVTOCI as well as contract assets. The Group always recognizes lifetime Expected Credit Loss (“ECL”) for trade receivables and contract assets. For all other financial instruments, the Group recognizes lifetime ECL when there has been a significant increase in credit risk since initial recognition. If, on the other hand, the credit risk on the financial instrument has not increased significantly since initial recognition, the Group measures the loss allowance for that financial instrument at an amount equal to 12-month ECL. Expected credit losses reflect the weighted average of credit losses with the respective risks of a default occurring as the weights. Lifetime ECL represents the expected credit losses that will result from all possible default events over the expected life of a financial instrument. In contrast, 12-month ECL represents the portion of lifetime ECL that is expected to result from default events on a financial instrument that are possible within 12 months after the reporting date. The Group recognizes an impairment gain or loss in profit or loss for all financial instruments with a corresponding adjustment to their carrying amount through a loss allowance account, except for investments in debt instruments that are measured at FVTOCI, for which the loss allowance is recognized in other comprehensive income and does not reduce the carrying amount of the financial asset. Prior to 2018 Financial assets, other than those at FVTPL, are assessed for indicators of impairment at each balance sheet date. Financial assets are considered to be impaired when there is objective evidence that, as a result of one or more events that occurred after the initial recognition of the financial assets, the estimated future cash flows of the investments have been affected. For financial assets carried at amortized cost, such as trade receivables and other receivables, assets that are assessed not to be impaired individually are, further, assessed for impairment on a collective basis. ASE and its subsidiaries assess the collectability of receivables based on their past experience of collecting payments and observable changes that correlate with default on receivables. For financial assets carried at amortized cost, the amount of the impairment loss recognized is the difference between the assets’ carrying amounts and the present value of estimated future cash flows, discounted at the financial assets’ original effective interest rates. If, in a subsequent period, the amount of the impairment loss decreases and the decreases can be objectively related to an event occurring after the impairment loss recognized, the previously recognized impairment loss is reversed either directly or by adjusting an allowance account through profit or loss. The reversal shall not result in carrying amounts of financial assets that exceed what the amortized cost would have been at the date the impairment is reversed. For any available-for-sale equity investments, a significant or prolonged decline in the fair value of the security below its cost is considered to be objective evidence of impairment. When an available-for-sale financial asset is considered to be impaired, cumulative gains or losses previously recognized in other comprehensive income are reclassified to profit or loss in the period. In respect of available-for-sale equity securities, impairment loss previously recognized in profit or loss is not reversed through profit or loss. Any increase in fair value subsequent to impairment is recognized in other comprehensive income. In respect of available-for-sale debt securities, impairment loss is subsequently reversed through profit or loss if an increase in the fair value of the investment can be objectively related to an event occurring after the recognition of the impairment loss. The carrying amount of the financial asset is reduced by the impairment loss directly for all financial assets with the exception of trade and other receivables where the carrying amount is reduced through the use of an allowance account. When trade and other receivables are considered uncollectible, they are written off against the allowance account. Subsequent recoveries of amounts previously written off are credited against the allowance account. Changes in the carrying amount of the allowance account are recognized in profit or loss except for uncollectible trade receivables and other receivables that are written off against the allowance account. c) Derecognition of financial assets The Group derecognizes a financial asset only when the contractual rights to the cash flows from the asset expire or when it transfers the financial asset and substantially all the risks and rewards of ownership of the asset to another entity. Before 2018, on derecognition of a financial asset in its entirety, the difference between the asset’s carrying amount and the sum of the consideration received and receivable and the cumulative gain or loss which had been recognized in other comprehensive income is recognized in profit or loss. Starting from 2018, on derecognition of a financial asset at amortized cost in its entirety, the difference between the asset’s carrying amount and the sum of the consideration received and receivable is recognized in profit or loss. On derecognition of an investment in a debt instrument at FVTOCI, the difference between the asset’s carrying amount and the sum of the consideration received and receivable and the cumulative gain or loss which had been recognized in other comprehensive income is recognized in profit or loss. However, on derecognition of an investment in an equity instrument at FVTOCI, the difference between the asset’s carrying amount and the sum of the consideration received and receivable is recognized in profit or loss, and the cumulative gain or loss which had been recognized in other comprehensive income is transferred directly to retained earnings, without recycling through profit or loss. 2) Equity instruments Debt and equity instruments issued by a group entity are classified as either financial liabilities or as equity in accordance with the substance of the contractual arrangements and the definitions of a financial liability and an equity instrument. Equity instruments issued by a group entity are recognized at the proceeds received, net of direct issue costs. Repurchase of the Company’s own equity instruments is recognized in and deducted directly from equity. No gain or loss is recognized in profit or loss on the purchase, sale, issue or cancellation of the Company’s own equity instruments. 3) Financial liabilities Financial liabilities are measured either at amortized cost using the effective interest method or at FVTPL. Financial liabilities measured at FVTPL are held for trading. Financial liabilities held for trading are stated at fair value, with any gain or loss arising on remeasurement recognized in profit or loss. The net gain or loss recognized in profit or loss incorporates any interest or dividend paid on the financial liability. Fair value is determined in the manner described in Note 36. The Group derecognizes financial liabilities only when the Group’s obligations are discharged, cancelled or expired. The difference between the carrying amount of the financial liability derecognized and the consideration paid and payable, including any non-cash assets transferred or liabilities assumed, is recognized in profit or loss. 4) Derivative financial instruments The Group enters into a variety of derivative financial instruments to manage its exposure to interest rate and foreign exchange rate risks, including forward exchange contracts, swap contracts, interest rate swap contracts and foreign currency option contracts. Derivatives are initially recognized at fair value at the date on which the derivative contracts are entered into and are subsequently remeasured to their fair value at the end of each reporting period. The resulting gain or loss is recognized in profit or loss immediately unless the derivative is designated and effective as a hedging instrument; in which event, the timing of the recognition in profit or loss depends on the nature of the hedging relationship. When the fair value of a derivative financial instrument is positive, the derivative is recognized as a financial asset; when the fair value of a derivative financial instrument is negative, the derivative is recognized as a financial liability. Before 2018, derivatives embedded in non-derivative host contracts were treated as separate derivatives when they met the definition of a derivative; their risks and characteristics were not closely related to those of the host contracts; and the contracts were not measured at FVTPL. Starting from 2018, derivatives embedded in hybrid contracts that contain financial asset hosts that is within the scope of IFRS 9 are not separated; instead, the classification is determined in accordance with the entire hybrid contract. Derivatives embedded in non-derivative host contracts that are not financial assets that is within the scope of IFRS 9 (e.g. financial liabilities) are treated as separate derivatives when they meet the definition of a derivative, their risks and characteristics are not closely related to those of the host contracts and the host contracts are not measured at FVTPL. 5) Convertible bonds a) Convertible bonds contain conversion option classified as an equity The component parts of compound instruments (convertible bonds) issued by the Group are classified separately as financial liabilities and equity in accordance with the substance of the contractual arrangements and the definitions of a financial liability and an equity instrument. On initial recognition, the fair value of the liability component is estimated using the prevailing market interest rate for similar non-convertible instruments. This amount is recorded as a liability on an amortized cost basis using the effective interest method until extinguished upon conversion or the instrument’s maturity date. Any embedded derivative liability is measured at fair value. The conversion option classified as equity is determined by deducting the amount of the liability component from the fair value of the compound instrument as a whole. This is recognized and included in equity, net of income tax effects, and is not subsequently remeasured. In addition, the conversion option classified as equity will remain in equity until the conversion option is exercised, in which case, the balance recognized in equity will be transferred to capital surplus - share premium. When the conversion option remains unexercised at maturity, the balance recognized in equity will be transferred to capital surplus - share premium. Transaction costs that relate to the issuance of the convertible bonds are allocated to the liability and equity components in proportion to the allocation of the gross proceeds. Transaction costs relating to the equity component are recognized directly in equity. Transaction costs relating to the liability component are included in the carrying amount of the liability component. b) Convertible bonds contain conversion option classified as a liability The conversion options component of the convertible bonds issued by the Group that will be settled other than by the exchange of a fixed amount of cash or other financial asset for a fixed number of the Group’s own equity instruments is classified as derivative financial liabilities. On initial recognition, the derivative financial liabilities component of the convertible bonds is recognized at fair value, and the initial carrying amount of the component of non-derivative financial liabilities is determined by deducting the amount of derivative financial liabilities from the fair value of the hybrid instrument as a whole. In subsequent periods, the non-derivative financial liabilities component of the convertible bonds is measured at amortized cost using the effective interest method. The derivative financial liabilities component is measured at fair value and the changes in fair value are recognized in profit or loss. Transaction costs that relate to the issue of the convertible bonds are allocated to the derivative financial liabilities component and the non-derivative financial liabilities component in proportion to their relative fair values. Transaction costs relating to the derivative financial liabilities component are recognized immediately in profit or loss. Transaction costs relating to the non-derivative financial liabilities component are included in the carrying amount of the liability component.
Hedge Accounting	o. Hedge Accounting The Group designates certain hedging instruments, which include derivatives, embedded derivatives and non-derivatives in respect of foreign currency risk, as either fair value hedges or cash flow hedges. 1) Fair value hedges Changes in the fair value of derivatives that are designated and qualify as fair value hedges are recognized in profit or loss immediately, together with any changes in the fair value of the hedged asset or liability that are attributable to the hedged risk. The change in the fair value of the hedging instrument and the change in the hedged item attributable to the hedged risk are recognized in profit or loss in the line item relating to the hedged item. Before 2018, hedge accounting was discontinued prospectively when ASE and its subsidiaries revoked the designated hedging relationship; when the hedging instrument expired or was sold, terminated, or exercised; or when the hedging instrument no longer met the criteria for hedge accounting. From 2018, the Group discontinues hedge accounting only when the hedging relationship cease to meet the qualifying criteria; for instance, when the hedging instrument expires or is sold, terminated, or exercised. 2) Cash flow hedges The effective portion of changes in the fair value of derivatives that are designated and qualify as cash flow hedges is recognized in other comprehensive income. The gain or loss relating to the ineffective portion are recognized immediately in profit or loss. The associated gains or losses that were recognized in other comprehensive income are reclassified from equity to profit or loss as a reclassification adjustment in the line item relating to the hedged item in the same period when the hedged item affects profit or loss. If a hedge of a forecasted transaction subsequently results in the recognition of a non-financial asset or a non-financial liability, the associated gains and losses that were recognized in other comprehensive income are removed from equity and included in the initial cost of the non-financial asset or non-financial liability. Before 2018, hedge accounting was discontinued prospectively when ASE and its subsidiaries revoked the designated hedging relationship; when the hedging instrument expired or was sold, terminated, or exercised; or when the hedging instrument no longer met the criteria for hedge accounting. From 2018, the Group discontinues hedge accounting only when the hedging relationship cease to meet the qualifying criteria; for instance, when the hedging instrument expires or is sold, terminated, or exercised. The cumulative gain or loss on the hedging instrument that has been previously recognized in other comprehensive income from the period when the hedge was effective remains separately in equity until the forecast transaction occurs. When a forecast transaction is no longer expected to occur, the gain or loss accumulated in equity is recognized immediately in profit or loss.
Revenue Recognition	p. Revenue recognition 2018 The Group identifies the contracts with customers, allocates transaction prices to performance obligations and, when performance obligations are satisfied, recognizes revenues at fixed amounts as agreed in the contracts with taking estimated volume discounts into consideration. For contracts where the period between the date on which the Group transfers a promised good or service to a customer and the date on which the customer pays for that good or service is one year or less, the Group does not adjust the promised amount of consideration for the effects of a significant financing component. Operating revenues The Group’s operating revenues include revenues from sale of goods and services as well as sale and leasing of real estate properties. When customers control goods as they are manufactured in progress, the Group measures progress on the basis of input incurred relative to the total input and recognizes revenues and contract assets over time. Those contract assets are then reclassified to trade receivables at the point at which they are invoiced to customers. The Group recognizes revenues and trade receivables when the goods are shipped or the goods are delivered to the customers’ specific locations because it is the time when customers have full discretion over the manner of distribution and price to sell the goods, has the primary responsibility for sales to future customers, and bears the risks of obsolescence. The revenues from sale of real estate properties are recognized when customers purchase real estate properties and complete the transfer procedures. The revenues from leasing real estate properties are recognized during leasing periods on the straight-line basis. Prior to 2018 Revenue is measured at the fair value of the consideration received or receivable take into account of estimated customer returns, rebates and other similar allowances. 1) Revenue from sale of goods and real estate properties Revenue from the sale of goods and real estate properties is recognized when all the following conditions are satisfied: a) ASE and its subsidiaries has transferred to the buyer the significant risks and rewards of ownership of the goods; b) A SE and its subsidiaries usually associated with ownership nor effective control over the goods sold; c) The amount of revenue can be measured reliably; d) It is probable that the economic benefits associated with the transaction will flow to A SE and its subsidiaries e) The costs incurred or to be incurred in respect of the transaction can be measured reliably. 2) Revenue from rendering of services Service income is recognized when services are rendered. 3) Revenue from dividend and interest income Dividend income from investments and interest income from financial assets are recognized when they are probable that the economic benefits will flow to ASE and its subsidiaries and the amount of income can be reliably measured. Interest income is accrued on a time basis, by reference to the principal outstanding and at the effective interest rate applicable.
Leasing	q. Leasing Leases are classified as finance leases whenever the terms of the lease transfer substantially all the risks and rewards of ownership to the lessee. All other leases are classified as operating leases. The Group as lessor Rental income from operating leases is recognized on a straight-line basis over the term of the relevant lease. The Group as lessee Assets held under finance leases are initially recognized as assets of the Group at their fair value at the inception of the lease or, if lower, at the present value of the minimum lease payments. The corresponding liability to the lessor is included in the consolidated balance sheets as a finance lease obligation. Operating lease payments are recognized as expenses on a straight-line basis over the lease term.
Borrowing Costs	r. Borrowing costs Borrowing costs directly attributable to the acquisition, construction or production of qualifying assets are added to the cost of those assets, until such time as the assets are substantially ready for their intended use or sale. Investment income earned on the temporary investment of specific borrowings pending their expenditure on qualifying assets is deducted from the borrowing costs eligible for capitalization. Other than stated above, all other borrowing costs are recognized in profit or loss in the period in which they are incurred.
Government grants	s. Government grants Government grants are not recognized until there is reasonable assurance that the Group will comply with the conditions attaching to them and that the grants will be received. Government grants are recognized in profit or loss on a systematic basis over the periods in which the Group recognizes as expenses the related costs for which the grants are intended to compensate. Specifically, government grants whose primary condition is that the Group should purchase, construct or otherwise acquire non-current assets are recognized as deferred revenue in the consolidated financial statements and transferred to profit or loss on a systematic and rational basis over the useful lives of the related assets. Government grants that are receivable as compensation for expenses or losses already incurred or for the purpose of giving immediate financial support to the Group with no future related costs are recognized in profit or loss in the period in which they become receivable.
Employee Benefits	t. Employee benefits a) Short-term employee benefits Liabilities recognized in respect of short-term employee benefits are measured at the undiscounted amount of the benefits expected to be paid in exchange for the related services. b) Retirement benefits Payments to defined contribution retirement benefit plans are recognized as expenses when employees have rendered services entitling them to the contributions. Defined benefit costs (including service cost, net interest and remeasurement) under the defined benefit retirement benefit plans are determined using the projected unit credit method. Service cost (including current service cost and past service cost) and net interest on the net defined benefit liability (asset) are recognized as employee benefits expense in the period they occur. Remeasurement, comprising actuarial gains and losses and the return on plan assets (excluding interest), is recognized in other comprehensive income in the period in which they occur. Remeasurement recognized in other comprehensive income is reflected immediately in retained earnings and will not be reclassified to profit or loss. Net defined benefit liability (asset) represents the actual deficit (surplus) in the Group’s defined benefit plan. Any surplus resulting from this calculation is limited to the present value of any refunds from the plans or reductions in future contributions to the plans.
Employee share options	u. Employee share options The fair value at the grant date of the employee share options is expensed on a straight-line basis over the vesting period, based on the Group’s best estimate of the number of options that are expected to ultimately vest, with a corresponding increase in capital surplus - employee share options and non-controlling interests. It is recognized as an expense in full at the grant date if vesting immediately. The grant date of issued ordinary shares for cash which are reserved for employees is the date on which the number of shares that the employees purchase is confirmed. At each balance sheet date, the Group reviews its estimate of the number of employee share options expected to vest. The impact of the revision of the original estimates is recognized in profit or loss such that the cumulative expense reflects the revised estimate, with a corresponding adjustment to the capital surplus - employee share options and non-controlling interests. The grant by the Company of its equity instruments to the employees of a subsidiary under options is treated as a capital contribution. The fair value of employee services received under the arrangement is measured by reference to the grant-date fair value and is recognized over the vesting period as an addition to the investment in the subsidiary, with a corresponding credit to capital surplus - employee share options.
Taxation	v. Taxation Income tax expense represents the sum of the tax currently payable and deferred tax. 1) Current tax According to the Income Tax Law of the R.O.C., an additional tax of unappropriated earnings is provided for as income tax in the year the shareholders approve to retain earnings. Adjustments of prior years’ tax liabilities are added to or deducted from the current year’s tax provision. 2) Deferred tax Deferred tax is recognized on temporary differences between the carrying amounts of assets and liabilities in the consolidated financial statements and the corresponding tax bases used in the computation of taxable profit. If a temporary difference arises from the initial recognition (other than in a business combination) of assets and liabilities in a transaction that affects neither the taxable profit nor the accounting profit, the resulting deferred tax asset or liability is not recognized. In addition, a deferred tax liability is not recognized on taxable temporary differences arising from the initial recognition of goodwill. Deferred tax liabilities are generally recognized for all taxable temporary differences. Deferred tax assets are generally recognized for all deductible temporary differences, unused loss carryforwards and unused tax credits for purchases of machinery and equipment to the extent that it is probable that taxable profits will be available against which those deductible temporary differences can be utilized. Deferred tax liabilities are recognized for taxable temporary differences associated with investments in subsidiaries and associates, except where the Group is able to control the reversal of the temporary differences and it is probable that the temporary difference will not reverse in the foreseeable future. Deferred tax assets arising from deductible temporary difference associated with such investments and interests are only recognized to the extent that it is probable that there will be sufficient taxable profits against which to utilize the benefits of the temporary differences and they are expected to reverse in the foreseeable future. The carrying amount of deferred tax assets is reviewed at each balance sheet date and reduced to the extent that it is no longer probable that sufficient taxable profits will be available to allow all or part of the assets to be recovered. A previously unrecognized deferred tax asset is also reviewed at each balance sheet date and recognized to the extent that it has become probable that future taxable profit will allow the deferred tax asset to be recovered. Deferred tax liabilities and assets are measured at the tax rates that are expected to apply in the period in which the liabilities are settled or assets are realized, based on tax rates (and tax laws) that have been enacted or substantively enacted by the balance sheet date. The measurement of deferred tax liabilities and assets reflects the tax consequences that would follow from the manner in which the Group expects, at the balance sheet date, to recover or settle the carrying amount of its assets and liabilities. 3) Current and deferred tax for the year Current and deferred tax are recognized in profit or loss, except when they relate to items that are recognized in other comprehensive income or directly in equity, in which case, the current and deferred tax are also recognized in other comprehensive income or directly in equity, respectively. Where current tax or deferred tax arises from the initial accounting for a business combination, the tax effect is included in the accounting for the business combination.
U.S. Dollar Amounts	w. U.S. Dollar Amounts A translation of the consolidated financial statements into U.S. dollars is included solely for the convenience of the readers, and has been translated from New Taiwan dollar (NT$) at the exchange rate as set forth in the statistical release by the U.S. Federal Reserve Board of the United States, which was NT$30.61 to US$1.00 as of December 31, 2018. The translation should not be construed as a representation that the NT$ amounts have been, could have been, or could in the future be, converted into U.S. dollars at this or any other rate of exchange.

Application of New and Revise_2

Application of New and Revised International Financial Reporting Standards as Issued by the International Accounting Standards Board ("IASB") ( Collectively, "IFRSs") (Tables)	12 Months Ended
	Dec. 31, 2018
IFRS 9 [member]
Statement [LineItems]
Summary of Financial Assets and Liabilities	The following table shows the original measurement categories and carrying amount under IAS 39 and the new measurement categories and carrying amount under IFRS 9 for each class of the Group’s financial assets and financial liabilities as of January 1, 2018. Measurement Category Carrying Amount Financial Assets IAS 39 IFRS 9 IAS 39 IAS 39 IFRS 9 IFRS 9 Remark NT$ US$ (Note 4) NT$ US$ (Note 4) Cash and cash equivalents Loans and receivables Amortized cost $ 46,078,066 $ 1,505,327 $ 46,078,066 $ 1,505,327 Derivatives Held for trading Mandatorily at fair value through profit or loss (“FVTPL”) 121,863 3,981 121,863 3,981 Equity instruments Held for trading Mandatorily at FVTPL 4,410,732 144,094 4,410,732 144,094 Available-for-sale Mandatorily at FVTPL 279,791 9,141 279,791 9,141 b) Available-for-sale Fair value through other comprehensive income (“FVTOCI”) - equity instruments 908,549 29,681 908,549 29,681 a) Open-end mutual funds Held for trading Mandatorily at FVTPL 589,976 19,274 589,976 19,274 Available-for-sale Mandatorily at FVTPL 23,825 778 23,825 778 b) Debt instruments Designated as at FVTPL Mandatorily at FVTPL 100,496 3,283 100,496 3,283 Other financial assets FVTOCI - debt instruments 1,000,000 32,669 1,080,000 35,283 d) Time deposits with original maturity of over three months, pledged time deposits and guarantee deposits Loans and receivables Amortized cost 405,520 13,248 405,520 13,248 c) Trade receivables and other receivables Loans and receivables Amortized cost 56,252,661 1,837,722 56,252,661 1,837,722 Financial Assets IAS 39 Carrying Amount as of January 1, 2018 Reclassifi- cations Remea- surements IFRS 9 Carrying Amount as of January 1, 2018 Retained Earnings Effect on January 1, 2018 Other Equity Effect on 2018 Remark NT$ NT$ NT$ NT$ NT$ NT$ FVTPL $ 5,223,067 Add: Reclassification from available-for-sale (IAS 39) - required reclassification - $ 303,616 $ - $ 110,648 $ (110,648 ) b) 5,223,067 303,616 - $ 5,526,683 110,648 (110,648 ) FVTOCI Debt instruments Add: Reclassification from other financial assets - 1,000,000 80,000 - 80,000 d) Equity instruments - 908,549 - 417,398 (417,398 ) a) - 1,908,549 80,000 1,988,549 417,398 (337,398 ) Investments accounted for using the equity method 48,753,751 - (2,586 ) 48,751,165 (163,579 ) 160,993 $ 53,976,818 $ 2,212,165 $ 77,414 $ 56,266,397 $ 364,467 $ (287,053 ) Financial Assets IAS 39 Carrying Amount as of January 1, 2018 Reclassifi- cations Remea- surements IFRS 9 Carrying Amount as of January 1, 2018 Retained Earnings Effect on January 1, 2018 Other Equity Effect on 2018 Remark US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) FVTPL $ 170,633 Add: Reclassification from available-for-sale (IAS 39) - required reclassification - $ 9,919 $ - $ 3,615 $ (3,615 ) b) 170,633 9,919 - $ 180,551 3,615 (3,615 ) FVTOCI Debt instruments Add: Reclassification from other financial assets - 32,669 2,614 - 2,614 d) Equity instruments - 29,682 - 13,636 (13,636 ) a) - 62,351 2,614 64,964 13,636 (11,022 ) Investments accounted for using the equity method 1,592,739 - (85 ) 1,592,655 (5,344 ) 5,259 $ 1,763,372 $ 72,270 $ 2,529 $ 1,838,170 $ 11,907 $ (9,378 ) a) Unquoted shares and limited partnership classified as available-for-sale are designated as at FVTOCI and the changes in fair value accumulated in other equity are transferred directly to retained earnings instead of being reclassified to profit or loss on disposal. Impairment losses previously recognized and accumulated in retained earnings are adjusted by the Group to record an increase in retained earnings and a decrease in other equity, unrealized gains or losses on financial assets at fair value through other comprehensive income, since no subsequent impairment assessment is required under IFRS 9; b) Quoted shares classified as available-for-sale are classified as at fair value through profit or loss under IFRS 9. Open-end mutual funds classified as available-for-sale are classified as at fair value through profit or loss under IFRS 9 because the contractual cash flows are not solely payments of principal and interest on the principal outstanding and they are not equity instruments. The Group reclassifies unrealized gains or losses on available-for-sale financial assets in other equity to retained earnings; c) Time deposits with original maturity of over three months, pledged time deposits and guarantee deposits are classified as measured at amortized cost under IFRS 9 because, on initial recognition, the contractual cash flows that are solely payments of principal and interest on the principal outstanding and these investments are held within a business model whose objective is to collect the contractual cash flows; and d) Debt investments with no active market are classified as at fair value through other comprehensive income under IFRS 9, because, on initial recognition, the contractual cash flows that are solely payments of principal and interest on the principal outstanding and these investments are held within a business model whose objective is achieved both by collecting contractual cash flows and selling financial assets. The Group adjusts those debt investments and other equity, unrealized gains or losses on financial assets at fair value through other comprehensive income, based on their fair value.
IFRS 16 [member]
Statement [LineItems]
Summary of Anticipated Impact on Assets, Liabilities and Equity	Anticipated impact on assets, liabilities and equity as of January 1, 2019 IAS 17 Carrying Amount as of December 31, 2018 Adjustments Arising from Initial Application of IFRS 16 IFRS 16 Carrying Amount as of January 1, 2019 NT$ NT$ NT$ Other financial assets - current $ 6,539,467 $ (31 ) $ 6,539,436 Other current assets 3,773,384 (385,014 ) 3,388,370 Long-term prepayments for lease 10,764,835 (10,764,835 ) - Property, plant and equipment 214,592,588 (277,079 ) 214,315,509 Right-of-use assets - 10,724,198 10,724,198 Investment properties 7,738,379 6,599,225 14,337,604 Other financial assets - non-current 1,044,294 (2,747 ) 1,041,547 Other intangible assets 30,897,700 (59,667 ) 30,838,033 Total effect on assets $ 275,350,647 $ 5,834,050 $ 281,184,697 Obligation under leases - current $ - $ 490,085 $ 490,085 Other current liabilities 5,984,156 (17,144 ) 5,967,012 Obligation under leases - non-current - 5,598,071 5,598,071 Other current liabilities - non-current 1,371,302 (236,962 ) 1,134,340 Total effect on liabilities $ 7,355,458 $ 5,834,050 $ 13,189,508 IAS 17 Carrying Amount as of December 31, 2018 Adjustments Arising from Initial Application of IFRS 16 IFRS 16 Carrying Amount as of January 1, 2019 US$ (Note 4) US$ (Note 4) US$ (Note 4) Other financial assets - current $ 213,638 $ (1 ) $ 213,637 Other current assets 123,273 (12,578 ) 110,695 Long-term prepayments for lease 351,677 (351,677 ) - Property, plant and equipment 7,010,539 (9,052 ) 7,001,487 Right-of-use assets - 350,349 350,349 Investment properties 252,806 215,591 468,397 Other financial assets - non-current 34,116 (90 ) 34,026 Other intangible assets 1,009,399 (1,949 ) 1,007,450 Total effect on assets $ 8,995,448 $ 190,593 $ 9,168,041 Obligation under leases - current $ - $ 16,010 $ 16,010 Other current liabilities 195,497 (560 ) 194,937 Obligation under leases - non-current - 182,884 182,884 Other current liabilities - non-current 44,799 (7,741 ) 37,058 Total effect on liabilities $ 240,296 $ 190,593 $ 430,889
Adoption of IFRS 15 [member]
Statement [LineItems]
Summary of Impact on Assets, Liabilities and Equity by Applying IFRS 15	The impact on assets, liabilities and equity as of January 1, 2018 from the initial application of IFRS 15 is set out below: IAS 18 Carrying Amount as of January 1, 2018 Adjustments Arising from Initial Application IFRS 15 Carrying Amount as of January 1, 2018 NT$ NT$ NT$ Inventories $ 24,260,911 $ (1,381,778 ) $ 22,879,133 Contract assets - current - 1,971,107 1,971,107 Investments accounted for using the equity method 48,753,751 40,139 48,793,890 Deferred tax assets 4,001,821 (7,287 ) 3,994,534 Total effect on assets $ 77,016,483 $ 622,181 $ 77,638,664 Current tax liabilities $ 7,619,328 $ 5,078 $ 7,624,406 Deferred tax liabilities 4,961,487 90,071 5,051,558 Total effect on liabilities $ 12,580,815 $ 95,149 $ 12,675,964 Retained earnings $ 73,718,545 $ 521,849 $ 74,240,394 Non-controlling interests 13,190,129 5,183 13,195,312 Total effect on equity $ 86,908,674 $ 527,032 $ 87,435,706 IAS 18 Carrying Amount as of January 1, 2018 Adjustments Arising from Initial Application IFRS 15 Carrying Amount as of January 1, 2018 US$ (Note 4) US$ (Note 4) US$ (Note 4) Inventories $ 792,581 $ (45,141 ) $ 747,440 Contract assets - current - 64,394 64,394 Investments accounted for using the equity method 1,592,739 1,311 1,594,050 IAS 18 Carrying Amount as of January 1, 2018 Adjustments Arising from Initial Application IFRS 15 Carrying Amount as of January 1, 2018 US$ (Note 4) US$ (Note 4) US$ (Note 4) Deferred tax assets $ 130,736 $ (238 ) $ 130,498 Total effect on assets $ 2,516,056 $ 20,326 $ 2,536,382 Current tax liabilities $ 248,916 $ 166 $ 249,082 Deferred tax liabilities 162,087 2,943 165,030 Total effect on liabilities $ 411,003 $ 3,109 $ 414,112 Retained earnings $ 2,408,316 $ 17,048 $ 2,425,364 Non-controlling interests 430,909 169 431,078 Total effect on equity $ 2,839,225 $ 17,217 $ 2,856,442 Had the Group applied IAS 18 in the current year, the following adjustments should have been made to reflect the line items and balances under IFRS 15. Impact on assets, liabilities and equity as of December 31, 2018 NT$ US$ (Note 4) Increase in inventories $ 2,313,269 $ 75,572 Decrease in contract assets - current (4,498,500 ) (146,961 ) Increase in trade receivables 1,073,368 35,066 Decrease in investments accounted for using the equity method (37,312 ) (1,219 ) Increase in deferred tax assets 26,389 862 Decrease in assets $ (1,122,786 ) $ (36,680 ) Decrease in current tax liabilities $ (47,028 ) $ (1,536 ) Decrease in deferred tax liabilities (141,934 ) (4,637 ) Decrease in liabilities $ (188,962 ) $ (6,173 ) Decrease in retained earnings $ (933,310 ) $ (30,490 ) Decrease in non-controlling interests (514 ) (17 ) Decrease in equity $ (933,824 ) $ (30,507 ) Impact on total comprehensive income for the year ended December 31, 2018 NT$ US$ (Note 4) Decrease in operating revenues $ (475,155 ) $ (15,523 ) Decrease in operating costs $ (101,964 ) $ (3,331 ) Increase in share of profit of associates and joint ventures $ 2,828 $ 92 Decrease in income tax expense $ (81,908 ) $ (2,676 ) Decrease in net profit and total comprehensive income for the year $ (406,792 ) $ (13,290 ) Increase (decrease) in net profit and total comprehensive income attributable to: Owners of the Company $ (411,461 ) $ (13,442 ) Non-controlling interests 4,669 152 $ (406,792 ) $ (13,290 ) Impact on earnings per share: Decrease in basic earnings per share $ (0.10 ) $ (0.00 ) Decrease in diluted earnings per share $ (0.10 ) $ (0.00 )

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Subsidiaries	2) Subsidiaries included in consolidated financial statements were as follows: Establishment and Percentage of Ownership (%) December 31 Name of Investee Main Businesses Operating Location 2017 2018 ASE Engaged in the packaging and testing of semiconductors Kaohsiung, R.O.C. 100.0 100.0 A.S.E. Holding Limited Holding company Bermuda 100.0 100.0 J & R Holding Limited (“J&R Holding”) Holding company Bermuda 100.0 100.0 Innosource Limited Holding company British Virgin Islands 100.0 100.0 Omniquest Industrial Limited Holding company British Virgin Islands 100.0 100.0 ASE Marketing & Service Japan Co., Ltd. Engaged in marketing and sales services Japan 100.0 100.0 ASE Test, Inc. Engaged in the testing of semiconductors Kaohsiung, R.O.C. 100.0 100.0 Luchu Development Corporation Engaged in the development of real estate properties Taipei, R.O.C. 86.1 86.1 TLJ Intertech Inc. (“TLJ”) Engaged in information software services Taipei, R.O.C. 60.0 60.0 MingFung Information Service Corp., Ltd. Engaged in information software services, and was established in May 2018. Taipei, R.O.C. - 100.0 Alto Enterprises Limited Holding company British Virgin Islands 100.0 100.0 Super Zone Holdings Limited Holding company Hong Kong 100.0 100.0 ASE (Kun Shan) Inc. Engaged in the packaging and testing of semiconductors Kun Shan, China 100.0 100.0 ASE Investment (Kun Shan) Limited Holding company Kun Shan, China 100.0 100.0 Advanced Semiconductor Engineering (China) Ltd. Will engage in the packaging and testing of semiconductors Shanghai, China 100.0 100.0 ASE Investment (Labuan) Inc. Holding company Malaysia 100.0 100.0 ASE Test Limited (“ASE Test”) Holding company Singapore 100.0 100.0 ASE (Korea) Inc. (“ASE Korea”) Engaged in the packaging and testing of semiconductors Korea 100.0 100.0 J&R Industrial Inc. Engaged in leasing equipment and investing activity Kaohsiung, R.O.C. 100.0 100.0 ASE Japan Co., Ltd. (“ASE Japan”) Engaged in the packaging and testing of semiconductors Japan 100.0 100.0 ASE (U.S.) Inc. After-sales service and sales support U.S.A. 100.0 100.0 Global Advanced Packaging Technology Limited Holding company British Cayman Islands 100.0 100.0 ASE WeiHai Inc. Engaged in the packaging and testing of semiconductors Shandong, China 100.0 100.0 Establishment and Percentage of Ownership (%) December 31 Name of Investee Main Businesses Operating Location 2017 2018 Suzhou ASEN Semiconductors Co., Ltd. (“ASEN”) Engaged in the packaging and testing of semiconductors Suzhou, China 60.0 70.0 Anstock Limited Engaged in financing activity British Cayman Islands 100.0 100.0 Anstock II Limited Engaged in financing activity British Cayman Islands 100.0 100.0 ASE (Shanghai) Inc. Engaged in the production of substrates Shanghai, China 100.0 100.0 ASE Corporation Holding company British Cayman Islands 100.0 100.0 ASE Mauritius Inc. Holding company Mauritius 100.0 100.0 ASE Labuan Inc. Holding company Malaysia 100.0 100.0 Shanghai Ding Hui Real Estate Development Co., Ltd. Engaged in the development, construction and sale of real estate properties Shanghai, China 100.0 100.0 Shanghai Ding Qi Property Management Co., Ltd. Engaged in the management of real estate properties Shanghai, China 100.0 100.0 Advanced Semiconductor Engineering (HK) Limited Engaged in the trading of substrates Hong Kong 100.0 100.0 Shanghai Ding Wei Real Estate Development Co., Ltd. Engaged in the development, construction and leasing of real estate properties Shanghai, China 100.0 100.0 Shanghai Ding Yu Real Estate Development Co., Ltd. Engaged in the development, construction and leasing of real estate properties Shanghai, China 100.0 100.0 Shanghai Ding Fan Department Store Co., Ltd. Engaged in department store business Shanghai, China 100.0 100.0 Kun Shan Ding Hong Real Estate Development Co., Ltd. Engaged in the development, construction and leasing of real estate properties Kun Shan, China 100.0 100.0 Shanghai Ding Xu Property Management Co., Ltd. Engaged in the management of real estate properties Shanghai, China 100.0 100.0 ASE Electronics Inc. Engaged in the production of substrates Kaohsiung, R.O.C. 100.0 100.0 ASE Test Holdings, Ltd. Holding company British Cayman Islands 100.0 100.0 ASE Holdings (Singapore) Pte. Ltd. Holding company Singapore 100.0 100.0 ASE Singapore Pte. Ltd. Engaged in the packaging and testing of semiconductors Singapore 100.0 100.0 ISE Labs, Inc. Engaged in the testing of semiconductors U.S.A. 100.0 100.0 ASE Electronics (M) Sdn. Bhd. Engaged in the packaging and testing of semiconductors Malaysia 100.0 100.0 ASE Assembly & Test (Shanghai) Limited Engaged in the packaging and testing of semiconductors Shanghai, China 100.0 100.0 Establishment and Percentage of Ownership (%) December 31 Name of Investee Main Businesses Operating Location 2017 2018 ASE Trading (Shanghai) Ltd. Liquidated in December 2018 Shanghai, China 100.0 - ISE Labs, China, Ltd. Engaged in the testing of semiconductors, and was established in October 2018 Shanghai, China - 100.0 Wuxi Tongzhi Microelectronics Co., Ltd. Engaged in the packaging and testing of semiconductors Wuxi, China 100.0 100.0 USI Global Engaged in investing activities, and was established in November 2018 and then dissolved in January 2019 Nantou, R.O.C. - 100.0 USIINC Engaged in investing activity Nantou, R.O.C. 99.2 100.0 Huntington Holdings International Co., Ltd. Holding company British Virgin Islands 99.2 100.0 Unitech Holdings International Co., Ltd. (“UHI”) Holding company British Virgin Islands 99.2 100.0 Real Tech Holdings Limited Holding company British Virgin Islands 99.2 100.0 Universal ABIT Holding Co., Ltd. In the process of liquidation British Cayman Islands 99.2 100.0 Rising Capital Investment Limited Holding company British Virgin Islands 99.2 100.0 Rise Accord Limited Holding company British Virgin Islands 99.2 100.0 Universal Scientific Industrial (Kunshan) Co., Ltd. Engaged in the manufacturing and sale of computer assistance system and related peripherals Kun Shan, China 99.2 100.0 USI Enterprise Limited (“USIE”) Engaged in the services of investment advisory and warehousing management Hong Kong 96.9 95.4 Universal Scientific Industrial (Shanghai) Co., Ltd. (“USISH”) Engaged in the designing, manufacturing and sale of electronic components Shanghai, China 75.8 74.6 Universal Global Technology Co., Limited Holding company Hong Kong 75.8 74.6 Universal Global Technology (Kunshan) Co., Ltd. Engaged in the designing and manufacturing of electronic components Kun Shan, China 75.8 74.6 Universal Global Technology (Shanghai) Co., Ltd. Engaged in the processing and sales of computer and communication peripherals as well as business in import and export of goods and technology Shanghai, China 75.8 74.6 Universal Global Electronics (Shanghai) Co., Ltd. Engaged in the sale of electronic components and telecommunications equipment Shanghai, China 75.8 74.6 Establishment and Percentage of Ownership (%) December 31 Name of Investee Main Businesses Operating Location 2017 2018 USI America Inc. Engaged in the manufacturing and processing of motherboards and wireless network communication and provision of related technical service U.S.A. 75.8 74.6 Universal Global Industrial Co., Limited Engaged in manufacturing, trading and investing activity Hong Kong 75.8 74.6 Universal Global Scientific Industrial Co., Ltd. (“UGTW”) Engaged in the manufacturing of components of telecomm and cars and provision of related R&D services Nantou, R.O.C. 75.8 74.6 Universal Scientific Industrial De Mexico S.A. De C.V. Engaged in the assembling of motherboards and computer components Mexico 75.8 74.6 USI Japan Co., Ltd. Engaged in the manufacturing and sale of computer peripherals, integrated chip and other related accessories Japan 75.8 74.6 USI Electronics (Shenzhen) Co., Ltd. Engaged in the design, manufacturing and sale of motherboards and computer peripherals Shenzhen, China 75.8 74.6 Universal Global Electronics Co., Ltd. Engaged in accepting and outsourcing orders as well as sales of electronic components and service of technical advisory, and was established in February 2018 Hong Kong - 74.6 Universal Scientific Industrial Co., Ltd. (“USI”) Engaged in the manufacturing, processing and sale of computers, computer peripherals and related accessories Nantou, R.O.C. 75.5 74.4 SPIL Engaged in the assembly, testing and turnkey services of integrated circuits Taichung, R.O.C. - 100.0 SPIL (B.V.I.) Holding Limited Engaged in investing activities British Virgin Islands - 100.0 Siliconware Investment Co., Ltd. Engaged in investing activities Taipei, R.O.C. - 100.0 Siliconware USA, Inc. Engaged in marketing activities U.S.A. - 100.0 Establishment and Percentage of Ownership (%) December 31 Name of Investee Main Businesses Operating Location 2017 2018 SPIL (Cayman) Holding Limited Engaged in investing activities British Cayman Islands - 100.0 Siliconware Technology (Suzhou) Limited Engaged in the packaging and testing of semiconductors Suzhou, China - 70.0 Siliconware Electronics (Fujian) Co., Limited Engaged in the packaging and testing of semiconductors Fujian, China - 100.0

Cash and Cash Equivalents (Tabl

Cash and Cash Equivalents (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Cash and Cash Equivalents	December 31 2017 2018 NT$ NT$ US$ (Note 4) Cash on hand $ 8,404 $ 7,940 $ 259 Checking accounts and demand deposits 39,697,319 32,329,820 1,056,185 Cash equivalents 6,372,343 19,180,676 626,615 $ 46,078,066 $ 51,518,436 $ 1,683,059

Financial Instruments at Fair_2

Financial Instruments at Fair Value Through Profit or Loss (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Financial Instruments at Fair Value Through Profit or Loss	December 31 2017 2018 NT$ NT$ US$ (Note 4) Financial assets designated as at FVTPL Private-placement convertible bonds $ 100,496 $ - $ - Financial assets held for trading Quoted ordinary shares $ 4,410,732 $ - $ - Open-end mutual funds 589,976 - - Forward exchange contracts 61,325 - - Swap contracts 60,538 - - 5,122,571 - - Financial assets mandatorily classified as at FVTPL Derivative instruments (non-designated hedges) Swap contracts - 1,557,714 50,889 Forward exchange contracts - 32,070 1,048 Non-derivative financial assets Quoted ordinary shares - 5,151,255 168,287 Open-end mutual funds - 581,800 19,007 Unquoted preferred shares - 275,000 8,984 Private-placement funds - 200,123 6,537 Hybrid financial assets Private-placement convertible bonds - 100,496 3,283 - 7,898,458 258,035 5,223,067 7,898,458 258,035 Current 5,223,067 7,262,227 237,250 Non-current $ - $ 636,231 $ 20,785 December 31 2017 2018 NT$ NT$ US$ (Note 4) Financial liabilities held for trading Derivative instruments (non-designated hedging) Swap contracts $ 652,107 $ 29,058 $ 949 Forward exchange contracts 25,323 7,597 248 $ 677,430 $ 36,655 $ 1,197
Summary of Outstanding Contracts Not Accounted for Hedge Accounting	At each balance sheet date, the outstanding swap contracts not accounted for hedge accounting were as follows: Notional Amount Currency Maturity Period (In Thousands) December 31, 2017 Sell NT$/Buy US$ 2018.01-2018.12 NT$53,136,302/US$1,782,400 Sell US$/Buy CNY 2018.01 US$52,948/CNY349,800 Sell US$/Buy JPY 2018.02-2018.03 US$70,324/JPY7,870,000 Sell US$/Buy NT$ 2018.01 US$217,300/NT$6,505,767 December 31, 2018 Sell NT$/Buy US$ 2019.01-2019.12 NT$49,570,469/US$1,687,400 Sell US$/Buy CNY 2019.01 US$50,292/CNY349,800 Sell US$/Buy JPY 2019.01 US$54,203/JPY6,090,000 Sell US$/Buy NT$ 2019.01 US$208,800/NT$6,423,242 At each balance sheet date, the outstanding forward exchange contracts not accounted for hedge accounting were as follows: Notional Amount Currency Maturity Period (In Thousands) December 31, 2017 Sell NT$/Buy US$ 2018.01 NT$2,389,620/US$80,000 Sell US$/Buy CNY 2018.01-2018.04 US$125,000/CNY828,858 Sell US$/Buy EUR 2018.01 US$10,674/EUR9,000 Sell US$/Buy JPY 2018.01-2018.02 US$45,517/JPY5,111,101 Sell US$/Buy MYR 2018.01-2018.03 US$15,000/MYR61,859 Sell US$/Buy NT$ 2018.01 US$1,000/NT$30,142 Sell US$/Buy SGD 2018.01-2018.02 US$11,300/SGD15,305 Notional Amount December 31, 2018 Maturity Period (In Thousands) Sell NT$/Buy US$ 2019.01-2019.02 NT$2,453,540/US$80,000 Sell US$/Buy CNY 2019.01 US$29,000/CNY200,108 Sell US$/Buy EUR 2019.01 US$4,103/EUR3,600 Sell US$/Buy JPY 2019.01-2019.02 US$37,733/JPY4,231,754 Sell US$/Buy MYR 2019.01-2019.02 US$14,000/MYR58,430 Sell US$/Buy SGD 2019.01-2019.02 US$13,400/SGD18,391

Financial Assets at Fair Valu_2

Financial Assets at Fair Value Through Other Comprehensive Income - 2018 (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Financial Assets at Fair Value Through Other Comprehensive Income	December 31, 2018 NT$ US$ (Note 4) Investments in equity instruments at FVTOCI $ 580,399 $ 18,961 Investments in debt instruments at FVTOCI 1,016,924 33,222 $ 1,597,323 $ 52,183
Summary of Investments in Equity Instruments at Fair Value Through Other Comprehensive Income	a. Investments in equity instruments at FVTOCI December 31, 2018 NT$ US$ (Note 4) Unquoted ordinary shares $ 532,047 $ 17,381 Limited partnership 39,669 1,296 Unquoted preferred shares 8,683 284 $ 580,399 $ 18,961
Summary of Investments in Debt Instruments at Fair Value Through Other Comprehensive Income	b. Investments in debt instruments at FVTOCI December 31, 2018 NT$ US$ (Note 4) Unsecured subordinate corporate bonds $ 1,016,924 $ 33,222

Available-for-sale Financial _2

Available-for-sale Financial Assets - 2017 (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Available-for-sale Financial Assets	December 31, 2017 NT$ Unquoted ordinary shares $ 605,110 Quoted ordinary shares 279,791 Limited partnership 246,072 Unquoted preferred shares 57,367 Open-end mutual funds 23,825 1,212,165 Current 89,159 Non-current $ 1,123,006

Trade Receivables, Net (Tables)

Trade Receivables, Net (Tables)	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Summary of Trade Receivables, Net	December 31 2017 2018 NT$ NT$ US$ (Note 4) At amortized cost Gross carrying amount $ 55,265,607 $ 79,636,748 $ 2,601,658 Less: Allowance for impairment loss 64,901 155,389 5,077 $ 55,200,706 $ 79,481,359 $ 2,596,581
Summary of Loss Allowance of Trade Receivables Based on Group's Provision Matrix	The following table details the loss allowance of trade receivables based on the Group’s provision matrix. December 31, 2018 Not Past Due Overdue 1 to 30 days Overdue 31 to 90 Days Overdue Over 91 Days Individually Total NT$ NT$ NT$ NT$ NT$ NT$ Expected credit loss rate 0 % 0~10% 0~50% 1~100% 0~100% - Gross carrying amount $ 71,819,583 $ 6,537,819 $ 778,799 $ 405,707 $ 94,840 $ 79,636,748 Loss allowance (Lifetime ECL) (7,119 ) (4,463 ) (14,949 ) (40,080 ) (88,778 ) (155,389 ) Amortized cost $ 71,812,464 $ 6,533,356 $ 763,850 $ 365,627 $ 6,062 $ 79,481,359 Not Past Due Overdue 1 to 30 days Overdue 31 to 90 Days Overdue Over 91 Days Individually Total US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) Expected credit loss rate 0 % 0~10% 0~50% 1~100% 0~100% - Gross carrying amount $ 2,346,278 $ 213,585 $ 25,443 $ 13,254 $ 3,098 $ 2,601,658 Loss allowance (Lifetime ECL) (233 ) (147 ) (488 ) (1,309 ) (2,900 ) (5,077 ) Amortized cost $ 2,346,045 $ 213,438 $ 24,955 $ 11,945 $ 198 $ 2,596,581
Summary of Movements of Loss Allowance of Trade Receivables	The movements of the loss allowance of trade receivables were as follows: For the Year Ended December 31, 2018 NT$ US$ (Note 4) Balance at January 1, 2018 $ 64,901 $ 2,120 Net remeasurement of loss allowance 150,128 4,905 Acquisition through business combinations 3,482 114 Amounts written off (60,109 ) (1,964 ) Effects of foreign currency exchange differences (3,013 ) (98 ) Balance at December 31, 2018 $ 155,389 $ 5,077
Summary of Aging of Receivables Based on Past Due Date	Aging of receivables based on the past due date December 31, 2017 NT$ Not past due $ 49,599,512 1 to 30 days 4,986,491 31 to 90 days 562,200 More than 91 days 117,404 $ 55,265,607
Trade receivables [member]
Statement [LineItems]
Summary of Aging of Receivables Past Due but Not Impaired	Aging of receivables that were past due but not impaired December 31, 2017 NT$ 1 to 30 days $ 4,942,677 31 to 90 days 378,526 $ 5,321,203
Summary of Movement of Allowance for Doubtful Trade Receivables	Movement of the allowance for doubtful trade receivables Impaired Individually Impaired Collectively Total NT$ NT$ NT$ Balance at January 1, 2016 $ 39,046 $ 43,860 $ 82,906 Impairment losses reversed (21,501 ) (6,521 ) (28,022 ) Effect of foreign currency exchange differences (1,092 ) (83 ) (1,175 ) Balance at December 31, 2016 16,453 37,256 53,709 Impairment losses recognized 9,527 4,102 13,629 Amounts written off - (34 ) (34 ) Effect of foreign currency exchange differences (850 ) (1,553 ) (2,403 ) Balance at December 31, 2017 $ 25,130 $ 39,771 $ 64,901

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Inventories	December 31 2017 2018 NT$ NT$ US$ (Note 4) Finished goods $ 6,740,816 $ 7,680,083 $ 250,901 Work in process 3,452,332 3,195,478 104,393 Raw materials 12,625,502 23,250,801 759,582 Supplies 894,196 1,892,194 61,816 Raw materials and supplies in transit 548,065 608,895 19,892 $ 24,260,911 $ 36,627,451 $ 1,196,584

Inventories Related to Real E_2

Inventories Related to Real Estate Business (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Inventories Related to Real Estate Business	December 31 2017 2018 NT$ NT$ US$ (Note 4) Land and buildings held for sale $ 25,825 $ 20,734 $ 677 Construction in progress 8,106,166 8,252,348 269,597 Land held for construction 1,687,525 1,787,526 58,397 $ 9,819,516 $ 10,060,608 $ 328,671

Other Financial Assets (Tables)

Other Financial Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Other Financial Assets	December 31 2017 2018 NT$ NT$ US$ (Note 4) Time deposits with original maturity of over three months $ 405,520 $ 6,320,669 $ 206,490 Guarantee deposits 170,594 766,190 25,031 Pledged time deposits (Note 38) 59,456 496,847 16,231 Unsecured subordinate corporate bonds (Notes 8 and 9) 1,000,000 - - Others (Note 38) 7,270 55 2 1,642,840 7,583,761 247,754 Current 472,340 6,539,467 213,638 Non-current $ 1,170,500 $ 1,044,294 $ 34,116

Investments Accounted for Usi_2

Investments Accounted for Using the Equity Method (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Investments Accounted for Using the Equity Method	December 31 2017 2018 NT$ NT$ US$ (Note 4) Investments in associates $ 48,267,237 $ 9,131,814 $ 298,328 Investments in joint venture 486,514 180,494 5,896 $ 48,753,751 $ 9,312,308 $ 304,224
Summary of Investments in Associates Accounted for using the Equity Method	a. Investments in associates 1) Investments in associates accounted for using the equity method consisted of the following: Carrying Amount as of December 31 2017 2018 Operating NT$ NT$ US$ (Note 4) Name of Associate Main Business Location Material associate SPIL Engaged in the assembly, testing and turnkey services of integrated circuits R.O.C. $ 45,210,371 $ - $ - Associates that are not individually material Deca Technologies Inc. （ ） Holding company and the group engaged in manufacturing, development and marketing of wafer level packaging and interconnect technology British Cayman Islands 1,583,124 866,312 28,302 Hung Ching Development & Construction Co. (“HC”) Engaged in the development, construction and leasing of real estate properties R.O.C. 1,248,711 1,095,233 35,780 Carrying Amount as of December 31 2017 2018 Operating NT$ NT$ US$ (Note 4) Name of Associate Main Business Location Hung Ching Kwan Co. (“HCK”) Engaged in the leasing of real estate properties R.O.C. $ 309,630 $ 295,772 $ 9,663 Advanced Microelectronic Products Inc. (“AMPI”) Engaged in integrated circuit R.O.C. 215,550 184,134 6,015 ChipMOS Technologies Inc. (“ChipMOS”) Engaged in the packaging and testing of semiconductors R.O.C. - 4,237,982 138,451 Yann Yuan Investment Co., Ltd. (“Yann Yuan”) Engaged in investing activities R.O.C. - 2,752,530 89,923 48,567,386 9,431,963 308,134 Less: Deferred gain on transfer of land 300,149 300,149 9,806 $ 48,267,237 $ 9,131,814 $ 298,328 2) At each balance sheet date, the percentages of ownership held by the Group were as follows: December 31 2017 2018 SPIL 33.29 % - DECA 22.04 % 22.04 % HC 26.22 % 26.22 % HCK 27.31 % 27.31 % AMPI 38.76 % 38.76 % ChipMOS - 20.47 % Yann Yuan - 32.21 %
Summary of Fair Values of Investments in Associates with Available Published Price Quotation	3) Fair values (Level 1 inputs in terms of IFRS 13) of investments in associates with available published price quotation are summarized as follows: December 31 2017 2018 NT$ NT$ US$ (Note 4) SPIL $ 52,176,190 $ - $ - HC $ 1,695,156 $ 1,537,307 $ 50,222 AMPI $ 468,572 $ 369,925 $ 12,085 ChipMOS $ - $ 3,886,561 $ 126,970
Summarized Financial Information	4) Summarized financial information in respect of the Group’s material associate The summarized financial information below represents amounts shown in SPIL’s consolidated financial statements prepared in accordance with IFRSs and adjusted by the Group for equity method accounting purposes. December 31, 2017 NT$ Current assets $ 49,065,912 Non-current assets 101,693,417 Current liabilities (26,194,615 ) Non-current liabilities (27,213,266 ) Equity $ 97,351,448 Proportion of the Group’s ownership interest in SPIL 33.29 % Net assets attributable to the Group $ 32,408,297 Goodwill 12,802,074 Carrying amount $ 45,210,371 For the Year Ended December 31, 2016 For the Year Ended December 31, 2017 For the Period from January 1, 2018 through April 29, 2018 NT$ NT$ NT$ US$ (Note 4) Operating revenue $ 85,111,913 $ 83,554,385 $ 26,169,040 $ 854,918 Gross profit $ 15,027,247 $ 12,464,792 $ 4,421,493 $ 144,446 Profit before income tax $ 7,351,661 $ 4,347,810 $ 848,072 $ 27,706 Net profit $ 5,484,462 $ 2,822,231 $ 413,317 $ 13,503 Other comprehensive income (loss) (2,373,532 ) 579,057 633,879 20,708 Total comprehensive income $ 3,110,930 $ 3,401,288 $ 1,047,196 $ 34,211 Cash dividends received from SPIL $ 3,941,740 $ 1,815,275 $ - $ -
Summary of Aggregate Information of Associates that are Not Individually Material	5) Aggregate information of associates that are not individually material For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) The Group’s share of: Net profit (loss) $ (139,366 ) $ (190,532 ) $ 147,535 $ 4,820 Other comprehensive income (loss) (115,650 ) 59,676 (613,471 ) (20,042 ) Total comprehensive loss $ (255,016 ) $ (130,856 ) $ (465,936 ) $ (15,222 )
Summary of Aggregate Information of the Joint Venture that is Not Individually Material	3) Aggregate information of the Group’s joint venture that is not individually material For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) The Group’s share of net loss and total comprehensive loss $ (90,478 ) $ (184,366 ) $ (306,156 ) $ (10,002 )

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Property, Plant and Equipment	The carrying amounts of each class of property, plant and equipment were as follows: December 31 2017 2018 NT$ NT$ US$ (Note 4) Land $ 3,258,518 $ 10,165,969 $ 332,113 Buildings and improvements 58,272,864 78,963,937 2,579,678 Machinery and equipment 66,185,198 108,087,970 3,531,133 Other equipment 1,588,113 6,463,160 211,145 Construction in progress and machinery in transit 5,863,713 10,911,552 356,470 $ 135,168,406 $ 214,592,588 $ 7,010,539 For the year ended December 31, 2016 Land Buildings and improvements Machinery and equipment Other equipment Construction in progress and machinery in transit Total NT$ NT$ NT$ NT$ NT$ NT$ Cost Balance at January 1, 2016 $ 3,381,300 $ 94,447,932 $ 243,283,607 $ 7,722,408 $ 6,397,760 $ 355,233,007 Additions - 22,341 94,480 470,901 27,093,140 27,680,862 Disposals - (684,698 ) (5,956,179 ) (159,822 ) (268,782 ) (7,069,481 ) Reclassification - 5,110,102 19,661,732 691,276 (25,463,285 ) (175 ) Acquisitions through business combinations - - - 1,159 - 1,159 Effect of foreign currency exchange differences (16,287 ) (2,637,502 ) (8,882,884 ) (251,261 ) (45,291 ) (11,833,225 ) Balance at December 31, 2016 $ 3,365,013 $ 96,258,175 $ 248,200,756 $ 8,474,661 $ 7,713,542 $ 364,012,147 Accumulated depreciation and impairment Balance at January 1, 2016 $ - $ 34,646,878 $ 164,568,298 $ 5,907,414 $ 113,342 $ 205,235,932 Depreciation expenses - 5,114,263 22,983,290 864,061 - 28,961,614 Impairment losses recognized - 620 876,123 5,564 5,924 888,231 Disposals - (449,198 ) (5,544,489 ) (151,875 ) (100,049 ) (6,245,611 ) Reclassification - (5,123 ) 9,660 (4,537 ) - - Acquisitions through business combinations - - - 824 - 824 Effect of foreign currency exchange differences - (1,077,896 ) (7,392,888 ) (236,371 ) (1,929 ) (8,709,084 ) Balance at December 31, 2016 $ - $ 38,229,544 $ 175,499,994 $ 6,385,080 $ 17,288 $ 220,131,906 For the year ended December 31, 2017 Land Buildings and improvements Machinery and equipment Other equipment Construction in progress and machinery in transit Total NT$ NT$ NT$ NT$ NT$ NT$ Cost Balance at January 1, 2017 $ 3,365,013 $ 96,258,175 $ 248,200,756 $ 8,474,661 $ 7,713,542 $ 364,012,147 Additions - 350,434 102,301 130,659 23,094,288 23,677,682 Disposals - (609,294 ) (8,449,949 ) (763,937 ) (73,248 ) (9,896,428 ) Reclassification (35,965 ) 6,483,392 18,331,738 174,947 (25,428,464 ) (474,352 ) Effect of foreign currency exchange differences (70,530 ) (2,294,779 ) (4,986,843 ) (204,250 ) 557,595 (6,998,807 ) Balance at December 31, 2017 $ 3,258,518 $ 100,187,928 $ 253,198,003 $ 7,812,080 $ 5,863,713 $ 370,320,242 Accumulated depreciation and impairment Balance at January 1, 2017 $ - $ 38,229,544 $ 175,499,994 $ 6,385,080 $ 17,288 $ 220,131,906 Depreciation expenses - 5,156,558 22,722,307 746,422 - 28,625,287 Impairment losses recognized - 2,310 286,880 368 - 289,558 Disposals - (478,903 ) (7,540,654 ) (720,319 ) (17,288 ) (8,757,164 ) Reclassification - (210,080 ) 34,452 (24,117 ) - (199,745 ) Effect of foreign currency exchange differences - (784,365 ) (3,990,174 ) (163,467 ) - (4,938,006 ) Balance at December 31, 2017 $ - $ 41,915,064 $ 187,012,805 $ 6,223,967 $ - $ 235,151,836 For the year ended December 31, 2018 Land Buildings and improvements Machinery and equipment Other equipment Construction in progress and machinery in transit Total NT$ NT$ NT$ NT$ NT$ NT$ Cost Balance at January 1, 2018 $ 3,258,518 $ 100,187,928 $ 253,198,003 $ 7,812,080 $ 5,863,713 $ 370,320,242 Additions - 144,898 192,673 84,860 38,669,807 39,092,238 Disposals - (677,206 ) (26,493,282 ) (2,251,060 ) (34,902 ) (29,456,450 ) Reclassification - 5,388,709 32,060,513 2,148,211 (39,612,324 ) (14,891 ) Acquisition through business combinations (Note 30) 6,880,400 37,127,957 95,810,062 11,122,171 5,781,189 156,721,779 Effect of foreign currency exchange differences 27,051 (464,275 ) (929,579 ) (78,095 ) 244,069 (1,200,829 ) Balance at December 31, 2018 $ 10,165,969 $ 141,708,011 $ 353,838,390 $ 18,838,167 $ 10,911,552 $ 535,462,089 Land Buildings and improvements Machinery and equipment Other equipment Construction in progress and machinery in transit Total NT$ NT$ NT$ NT$ NT$ NT$ Accumulated depreciation and impairment Balance at January 1, 2018 $ - $ 41,915,064 $ 187,012,805 $ 6,223,967 $ - $ 235,151,836 Depreciation expenses - 6,325,948 31,751,251 1,816,587 - 39,893,786 Impairment losses recognized - 29,531 97,680 5,860 - 133,071 Disposals - (491,033 ) (25,704,778 ) (2,070,302 ) - (28,266,113 ) Reclassification - (265 ) - - - (265 ) Acquisition through business combinations (Note 30) - 15,097,920 53,210,063 6,428,174 - 74,736,157 Effect of foreign currency exchange differences - (133,091 ) (616,601 ) (29,279 ) - (778,971 ) Balance at December 31, 2018 $ - $ 62,744,074 $ 245,750,420 $ 12,375,007 $ - $ 320,869,501 Land Buildings and improvements Machinery and equipment Other equipment Construction in progress and machinery in transit Total US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) Cost Balance at January 1, 2018 $ 106,453 $ 3,273,046 $ 8,271,741 $ 255,213 $ 191,562 $ 12,098,015 Additions - 4,734 6,294 2,772 1,263,306 1,277,106 Disposals - (22,124 ) (865,511 ) (73,540 ) (1,140 ) (962,315 ) Reclassification - 176,044 1,047,387 70,180 (1,294,097 ) (486 ) Acquisition through business combinations (Note 30) 224,776 1,212,936 3,130,025 363,351 188,866 5,119,954 Effect of foreign currency exchange differences 884 (15,168 ) (30,368 ) (2,551 ) 7,973 (39,230 ) Balance at December 31, 2018 $ 332,113 $ 4,629,468 $ 11,559,568 $ 615,425 $ 356,470 $ 17,493,044 Accumulated depreciation and impairment Balance at January 1, 2018 $ $ 1,369,326 $ 6,109,533 $ 203,331 $ - $ 7,682,190 Depreciation expense - 206,663 1,037,283 59,346 - 1,303,292 Impairment losses recognized - 965 3,191 192 - 4,348 Disposals - (16,042 ) (839,751 ) (67,635 ) - (923,428 ) Reclassification - (9 ) - - - (9 ) Acquisition through business combinations (Note 30) - 493,235 1,738,323 210,003 - 2,441,561 Effect of foreign currency exchange differences - (4,348 ) (20,144 ) (957 ) - (25,449 ) Balance at December 31, 2018 $ - $ 2,049,790 $ 8,028,435 $ 404,280 $ - $ 10,482,505
Summary of Property, Plant and Equipment Useful Lives	Each class of property, plant and equipment was depreciated on a straight-line basis over the following useful lives: Buildings and improvements Main plant buildings 10-55 years Cleanrooms 10-20 years Others 3-20 years Machinery and equipment 2-10 years Other equipment 2-20 years

Investment Properties (Tables)

Investment Properties (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Investment Properties	Land Buildings and improvements Total NT$ NT$ NT$ Cost Balance at January 1, 2017 $ - $ - $ - Additions - 186,535 186,535 Disposals - (342 ) (342 ) Transferred from inventories related to real estate business and property, plant and equipment 35,965 8,114,110 8,150,075 Effects of foreign currency exchange differences - 106,482 106,482 Balance at December 31, 2017 $ 35,965 $ 8,406,785 $ 8,442,750 Accumulated depreciation and impairment Balance at January 1, 2017 $ - $ - $ - Depreciation expenses - 122,231 122,231 Disposals - (161 ) (161 ) Transferred from property, plant and equipment - 199,745 199,745 Effects of foreign currency exchange differences - 1,499 1,499 Balance at December 31, 2017 $ - $ 323,314 $ 323,314 Carrying amount at December 31, 2017 $ 35,965 $ 8,083,471 $ 8,119,436 Land Buildings and improvements Total NT$ NT$ NT$ Cost Balance at January 1, 2018 $ 35,965 $ 8,406,785 $ 8,442,750 Additions - 125,853 125,853 Transferred from property, plant and equipment - 14,891 14,891 Effects of foreign currency exchange differences - (137,739 ) (137,739 ) Balance at December 31, 2018 $ 35,965 $ 8,409,790 $ 8,445,755 Accumulated depreciation and impairment Balance at January 1, 2018 $ - $ 323,314 $ 323,314 Depreciation expenses - 392,667 392,667 Transferred from property, plant and equipment - 265 265 Effects of foreign currency exchange differences - (8,870 ) (8,870 ) Balance at December 31, 2018 $ - $ 707,376 $ 707,376 Carrying amount at December 31, 2018 $ 35,965 $ 7,702,414 $ 7,738,379 Land Buildings and improvements Total US$ (Note 4) US$ (Note 4) US$ (Note 4) Cost Balance at January 1, 2018 $ 1,175 $ 274,642 $ 275,817 Additions - 4,111 4,111 Transferred from property, plant and equipment - 487 487 Effects of foreign currency exchange differences - (4,500 ) (4,500 ) Balance at December 31, 2018 $ 1,175 $ 274,740 $ 275,915 Accumulated depreciation and impairment Balance at January 1, 2018 $ - $ 10,562 $ 10,562 Depreciation expenses - 12,828 12,828 Transferred from property, plant and equipment - 9 9 Effects of foreign currency exchange differences - (290 ) (290 ) Balance at December 31, 2018 $ - $ 23,109 $ 23,109 Carrying amount at December 31, 2018 $ 1,175 $ 251,631 $ 252,806
Summary of Investment Properties, Useful Lives	The investment properties were depreciated on a straight-line basis over the following useful lives: Main buildings 10-40 years Others 3-20 years

Goodwill (Tables)

Goodwill (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Goodwill	Cost Accumulated impairment Carrying amount NT$ NT$ NT$ Balance at January 1, 2016 $ 12,495,515 $ 1,988,996 $ 10,506,519 Acquisitions through business combinations (Note 30) 15,323 - 15,323 Effect of foreign currency exchange differences (31,533 ) - (31,533 ) Balance at December 31, 2016 12,479,305 1,988,996 10,490,309 Impairment losses recognized - 425,117 (425,117 ) Effect of foreign currency exchange differences (130,698 ) - (130,698 ) Balance at December 31, 2017 12,348,607 2,414,113 9,934,494 Cost Accumulated impairment Carrying amount NT$ NT$ NT$ Acquisition through business combinations (Note 30) $ 39,990,231 $ - $ 39,990,231 Effect of foreign currency exchange differences 49,721 - 49,721 Balance at December 31, 2018 $ 52,388,559 $ 2,414,113 $ 49,974,446 Cost Accumulated impairment Carrying amount US$ (Note 4) US$ (Note 4) US$ (Note 4) Balance at January 1, 2018 $ 403,418 $ 78,867 $ 324,551 Acquisition through business combinations (Note 30) 1,306,443 - 1,306,443 Effect of foreign currency exchange differences 1,624 - 1,624 Balance at December 31, 2018 $ 1,711,485 $ 78,867 $ 1,632,618
Summary of Carrying Amounts of Goodwill Allocated to Cash-generating Units	The carrying amounts of goodwill allocated to cash-generating units were as follows: December 31 2017 2018 Cash-generating units NT$ NT$ US$ (Note 4) Packaging segment $ 1,362,724 $ 35,729,371 $ 1,167,245 Testing segment 7,775,581 13,448,886 439,362 Others 796,189 796,189 26,011 $ 9,934,494 $ 49,974,446 $ 1, 632,618

Other Intangible Assets (Tables

Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Carrying Amounts of Each Class of Other Intangible Assets	The carrying amounts of each class of other intangible assets were as follows: December 31 2017 2018 NT$ NT$ US$ (Note 4) Customer relationships $ 113,776 $ 10,366,797 $ 338,673 Computer software 864,331 1,159,682 37,886 Patents and acquired specific technology 319,402 19,255,669 629,065 Others 109,356 115,552 3,775 $ 1,406,865 $ 30,897,700 $ 1,009,399 For the year ended December 31, 2016 Customer relationships Computer software Patents and acquired specific technology Others Total NT$ NT$ NT$ NT$ NT$ Cost Balance at January 1, 2016 $ 915,636 $ 3,338,360 $ 154,082 $ 193,338 $ 4,601,416 Additions (Note 37) - 372,188 301,351 1,605 675,144 Disposals or derecognization (41,099 ) (80,537 ) (1,310 ) - (122,946 ) Reclassification - - 786 - 786 Acquisitions through business combinations 41,099 - 64,380 30 105,509 Effect of foreign currency exchange differences - (77,782 ) (4,846 ) (2,581 ) (85,209 ) Balance at December 31, 2016 $ 915,636 $ 3,552,229 $ 514,443 $ 192,392 $ 5,174,700 Accumulated amortization Balance at January 1, 2016 $ 641,234 $ 2,385,038 $ 138,386 $ 54,665 $ 3,219,323 Amortization expense 121,412 345,836 24,154 17,421 508,823 Disposals or derecognization (41,099 ) (58,765 ) (1,310 ) - (101,174 ) Reclassification - - 786 - 786 Acquisitions through business combinations - - 483 23 506 Effect of foreign currency exchange differences - (63,407 ) (7,283 ) (135 ) (70,825 ) Balance at December 31, 2016 $ 721,547 $ 2,608,702 $ 155,216 $ 71,974 $ 3,557,439 For the year ended December 31, 2017 Customer relationships Computer software Patents and acquired specific technology Others Total NT$ NT$ NT$ NT$ NT$ Cost Balance at January 1, 2017 $ 915,636 $ 3,552,229 $ 514,443 $ 192,392 $ 5,174,700 Additions - 265,497 - 12,328 277,825 Disposals - (83,595 ) (123,744 ) (4,978 ) (212,317 ) Effect of foreign currency exchange differences - (47,679 ) (1,213 ) (988 ) (49,880 ) Balance at December 31, 2017 $ 915,636 $ 3,686,452 $ 389,486 $ 198,754 $ 5,190,328 Accumulated amortization Balance at January 1, 2017 $ 721,547 $ 2,608,702 $ 155,216 $ 71,974 $ 3,557,439 Amortization expense 80,313 316,580 43,493 17,280 457,666 Disposals - (72,481 ) (123,743 ) - (196,224 ) Effect of foreign currency exchange differences - (30,680 ) (4,882 ) 144 (35,418 ) Balance at December 31, 2017 $ 801,860 $ 2,822,121 $ 70,084 $ 89,398 $ 3,783,463 For the year ended December 31, 2018 Customer relationships Computer software Patents and acquired specific technology Others Total NT$ NT$ NT$ NT$ NT$ Cost Balance at January 1, 2018 $ 915,636 $ 3,686,452 $ 389,486 $ 198,754 $ 5,190,328 Additions - 528,883 - 8,776 537,659 Disposals - (95,358 ) (231 ) (4,000 ) (99,589 ) Acquisition through business combinations (Note 30) 11,000,000 274,868 20,200,000 32,800 31,507,668 Effect of foreign currency exchange differences - 6,200 (899 ) (332 ) 4,969 Balance at December 31, 2018 $ 11,915,636 $ 4,401,045 $ 20,588,356 $ 235,998 $ 37,141,035 Customer relationships Computer software Patents and acquired specific technology Others Total NT$ NT$ NT$ NT$ NT$ Accumulated amortization Balance at January 1, 2018 $ 801,860 $ 2,822,121 $ 70,084 $ 89,398 $ 3,783,463 Amortization expense 746,979 373,536 1,263,309 18,626 2,402,450 Disposals - (95,202 ) (231 ) (4,000 ) (99,433 ) Acquisition through business combinations (Note 30) - 137,799 - 15,483 153,282 Effect of foreign currency exchange differences - 3,109 (475 ) 939 3,573 Balance at December 31, 2018 $ 1,548,839 $ 3,241,363 $ 1,332,687 $ 120,446 $ 6,243,335 Customer relationships Computer software Patents and acquired specific technology Others Total US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) Cost Balance at January 1, 2018 $ 29,913 $ 120,433 $ 12,724 $ 6,493 $ 169,563 Additions - 17,278 - 287 17,565 Disposals - (3,115 ) (8 ) (131 ) (3,254 ) Acquisition through business combinations 359,359 8,980 659,915 1,072 1,029,326 Effect of foreign currency exchange differences - 202 (29 ) (11 ) 162 Balance at December 31, 2018 $ 389,272 $ 143,778 $ 672,602 $ 7,710 $ 1,213,362 Accumulated amortization Balance at January 1, 2018 $ 26,196 $ 92,196 $ 2,290 $ 2,921 $ 123,603 Amortization expense 24,403 12,203 41,271 608 78,485 Disposals - (3,110 ) (8 ) (131 ) (3,249 ) Acquisition through business combinations - 4,502 - 506 5,008 Effect of foreign currency exchange differences - 101 (16 ) 31 116 Balance at December 31, 2018 $ 50,599 $ 105,892 $ 43,537 $ 3,935 $ 203,963
Summary of Other Intangible Assets Useful Lives	Each class of other intangible assets was amortized on the straight-line basis over the following useful lives: Customer relationships 11 years Computer software 2-10 years Patents and acquired specific technology 5-15 years Others 5-32 years

Borrowings (Tables)

Borrowings (Tables)	12 Months Ended
	Dec. 31, 2018
Long Term Bank Loans [member]
Statement [LineItems]
Summary of Borrowings	1) Bank loans December 31 2017 2018 NT$ NT$ US$ (Note 4) Working capital bank loans Syndicated bank loans - repayable through May 2019 to May 2023, annual interest rates were 2.61% -2.70% and 1.80% as of December 31, 2017 and 2018, respectively $ 4,761,600 $ 55,000,000 $ 1,796,798 Others - repayable through February 2019 to October 2023, annual interest rates were 0.93%-2.10% and 0.75%-3.77% as of December 31, 2017 and 2018, respectively 23,941,947 75,533,354 2,467,604 Mortgage loans Repayable through July 2019 to June 2023, annual interest rates were 4.95%-5.39% and 5.39% as of December 31, 2017 and 2018 4,705,149 4,393,826 143,542 33,408,696 134,927,180 4,407,944 Less: unamortized arrangement fee 1,200 128,083 4,184 33,407,496 134,799,097 4,403,760 Less: current portion 8,261,625 10,779,034 352,141 $ 25,145,871 $ 124,020,063 $ 4,051,619
Longterm Bills Payable [member]
Statement [LineItems]
Summary of Borrowings	2) Long-term bills payable December 31 2017 2018 NT$ NT$ US$ (Note 4) China Bills Finance Corporation, repayable in February 2020, annual interest rate were 0.96% and 0.99% as of December 31, 2017 and 2018, respectively $ 1,000,000 $ 1,000,000 $ 32,669 International Bills Finance Corporation, repayable in March 2020, annual interest rate were 0.96% and %1.00% as of December 31, 2017 and 2018, respectively 1,000,000 1,000,000 32,669 Ta Ching Bills Finance Corporation, repayable in January 2020, annual interest rates was 0.98% as of December 31, 2018 - 1,100,000 35,936 2,000,000 3,100,000 101,274 Less: unamortized discounts 868 768 25 $ 1,999,132 $ 3,099,232 $ 101,249

Bonds Payable (Tables)

Bonds Payable (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Bonds Payable	December 31 2017 2018 NT$ NT$ US$ (Note 4) Unsecured domestic bonds Repayable at maturity in January 2021 and interest due annually with annual interest rate at 1.30% $ 7,000,000 $ 7,000,000 $ 228,683 Repayable at maturity in January 2023 and interest due annually with annual interest rate at 1.50% 2,000,000 2,000,000 65,338 Repayable at maturity in January 2022 and interest due annually with annual interest rate at 1.25% 3,700,000 3,700,000 120,876 Repayable at maturity in January 2024 and interest due annually with annual interest rate at 1.45% 4,300,000 4,300,000 140,477 December 31 2017 2018 NT$ NT$ US$ (Note 4) Unsecured convertible overseas bonds US$200,000 thousand (linked to New Taiwan dollar) $ 6,185,600 $ - $ - 23,185,600 17,000,000 555,374 Less: discounts on bonds payable 42,820 14,064 459 23,142,780 16,985,936 554,915 Less: current portion 6,161,197 - - $ 16,981,583 $ 16,985,936 $ 554,915

Other Payables (Tables)

Other Payables (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Other Payables	December 31 2017 2018 NT$ NT$ US$ (Note 4) Accrued salary and bonus $ 7,292,254 $ 10,591,202 $ 346,005 Payables for property, plant and equipment 4,623,268 7,995,634 261,210 Accrued employees’ compensation and remuneration to directors 2,568,880 3,038,417 99,262 Accrued employee insurance 657,176 875,638 28,606 Accrued utilities 417,257 427,106 13,953 Payables for patents and acquired specific technology (Note 37) 93,000 57,590 1,882 Others 5,726,052 8,018,295 261,950 $ 21,377,887 $ 31,003,882 $ 1,012,868

Retirement Benefit Plans (Table

Retirement Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Defined Benefit Plans Amounts Included in Consolidated Balance Sheets	4) The amounts included in the consolidated balance sheets arising from the Group’s obligation in respect of its defined benefit plans excluding those for executive managers were as follows: December 31 2017 2018 NT$ NT$ US$ (Note 4) Present value of the defined benefit obligation $ 7,910,638 $ 10,297,139 $ 336,398 Fair value of the plan assets (4,341,373 ) (5,492,123 ) (179,423 ) Present value of unfunded defined benefit obligation 3,569,265 4,805,016 156,975 Recorded under other payables (24,638 ) (18,791 ) (614 ) Recorded under other current assets 182,421 11,910 389 Net defined benefit liability $ 3,727,048 $ 4,798,135 $ 156,750
Summary of Movements in Net Defined Benefit Liability (Asset)	Movements in net defined benefit liability (asset) were as follows: Present Value of the Defined Benefit Obligation Fair Value of the Plan Assets Net Defined Benefit Liability (Asset) NT$ NT$ NT$ Balance at January 1, 2016 $ 7,973,676 $ (3,973,729 ) $ 3,999,947 Service cost Current service cost 329,838 - 329,838 Net interest expense (income) 167,111 (109,080 ) 58,031 Recognized in profit or loss 496,949 (109,080 ) 387,869 Remeasurement Return on plan assets (excluding amounts included in net interest) - 54,549 54,549 Actuarial loss arising from changes in financial assumptions 156,193 - 156,193 Actuarial loss arising from experience adjustments 200,723 - 200,723 Actuarial loss arising from changes in demographic assumptions 5,716 - 5,716 Recognized in other comprehensive income 362,632 54,549 417,181 Contributions from the employer - (807,232 ) (807,232 ) Benefits paid from the pension fund (308,471 ) 308,471 - Benefits paid from the Group (36,033 ) - (36,033 ) Present Value of the Defined Benefit Obligation Fair Value of the Plan Assets Net Defined Benefit Liability (Asset) NT$ NT$ NT$ Liabilities assumed in a business combination $ 535 $ (535 ) $ - Exchange differences on foreign plans (99,404 ) 110,189 10,785 Balance at December 31, 2016 8,389,884 (4,417,367 ) 3,972,517 Service cost Current service cost 278,412 - 278,412 Past service cost and gain on settlements (68,979 ) - (68,979 ) Net interest expense (income) 157,404 (103,741 ) 53,663 Recognized in profit or loss 366,837 (103,741 ) 263,096 Remeasurement Return on plan assets (excluding amounts included in net interest) - 52,124 52,124 Actuarial loss arising from changes in financial assumptions 56,860 - 56,860 Actuarial gain arising from experience adjustments (315,090 ) - (315,090 ) Actuarial loss arising from changes in demographic assumptions 762 - 762 Recognized in other comprehensive income (257,468 ) 52,124 (205,344 ) Contributions from the employer - (484,790 ) (484,790 ) Benefits paid from the pension fund (690,830 ) 690,830 - Benefits paid from the Group (96,575 ) - (96,575 ) Exchange differences on foreign plans 198,790 (78,429 ) 120,361 Balance at December 31, 2017 7,910,638 (4,341,373 ) 3,569,265 Service cost Current service cost 224,126 - 224,126 Net interest expense (income) 178,779 (122,709 ) 56,070 Recognized in profit or loss 402,905 (122,709 ) 280,196 Remeasurement Return on plan assets (excluding amounts included in net interest) - (16,589 ) (16,589 ) Actuarial gain arising from changes in financial assumptions (8,643 ) - (8,643 ) Actuarial loss arising from experience adjustments 302,499 - 302,499 Actuarial loss arising from changes in demographic assumptions 8,190 - 8,190 Actuarial loss arising from changes in other assumptions 22,723 - 22,723 Present Value of the Defined Benefit Obligation Fair Value of the Plan Assets Net Defined Benefit Liability (Asset) NT$ NT$ NT$ Recognized in other comprehensive income $ 324,769 $ (16,589 ) $ 308,180 Contributions from the employer - (364,237 ) (364,237 ) Benefits paid from the pension fund (541,989 ) 541,989 - Benefits paid from the Group (295,953 ) - (295,953 ) Business combinations 2,522,805 (1,210,524 ) 1,312,281 Exchange differences on foreign plans (26,036 ) 21,320 (4,716 ) Balance at December 31, 2018 $ 10,297,139 $ (5,492,123 ) $ 4,805,016 Present Value of the Defined Benefit Obligation Fair Value of the Plan Assets Net Defined Benefit Liability (Asset) US$ (Note 4) US$ (Note 4) US$ (Note 4) Balance at January 1, 2018 $ 258,433 $ (141,829 ) $ 116,604 Service cost Current service cost 7,322 - 7,322 Net interest expense (income) 5,841 (4,009 ) 1,832 Recognized in profit or loss 13,163 (4,009 ) 9,154 Remeasurement Return on plan assets (excluding amounts included in net interest) - (542 ) (542 ) Actuarial gain arising from changes in financial assumptions (282 ) - (282 ) Actuarial loss arising from experience adjustments 9,882 - 9,882 Actuarial loss arising from changes in demographic assumptions 268 - 268 Actuarial loss arising from changes in other assumptions 742 - 742 Recognized in other comprehensive income 10,610 (542 ) 10,068 Contributions from the employer - (11,899 ) (11,899 ) Benefits paid from the pension fund (17,706 ) 17,706 - Benefits paid from the Group (9,669 ) - (9,669 ) Business combinations 82,418 (39,547 ) 42,871 Exchange differences on foreign plans (851 ) 697 (154 ) Balance at December 31, 2018 $ 336,398 $ (179,423 ) $ 156,975
Summary of Fair Value of the Plan Assets by Major Categories	5) The fair value of the plan assets by major categories at each balance sheet date was as follows: December 31 2017 2018 NT$ NT$ US$ (Note 4) Cash $ 2,317,764 $ 2,340,903 $ 76,475 Debt instruments 691,619 902,886 29,497 Equity instruments 1,254,109 2,164,895 70,725 Others 77,881 83,439 2,726 Total $ 4,341,373 $ 5,492,123 $ 179,423
Summary of Key Assumptions Used for the Actuarial Valuations	8) The present value of the defined benefit obligation and the related current service cost and past service cost were measured using the Projected Unit Credit Method. Except the pension plans for executive managers, the key assumptions used for the actuarial valuations were as follows: December 31 2017 2018 Discount rates (%) 0.06-3.85 0.05-3.02 Expected rates of salary increase (%) 2.00-4.42 1.75-4.06
Summary of Sensitivity Analysis on Defined Obligations	The sensitivity analysis below has been determined based on reasonably possible changes of the respective assumptions occurring at each balance sheet date, while holding all other assumptions constant. December 31 2017 2018 NT$ NT$ US$ (Note 4) Discount Rate 0.5% higher $ (455,158 ) $ (555,181 ) $ (18,137 ) 0.5% lower $ 461,891 $ 603,089 $ 19,702 Expected rates of salary increase 0.5% higher $ 453,792 $ 591,712 $ 19,331 0.5% lower $ (444,493 ) $ (547,522 ) $ (17,887 )
Summary of Maturity Analysis of Undiscounted Pension Benefit	9) Maturity analysis of undiscounted pension benefit December 31 2017 2018 NT$ NT$ US$ (Note 4) No later than 1 year $ 291,152 $ 368,592 $ 12,042 Later than 1 year but not later than 5 years 1,551,496 1,886,738 61,638 Later than 5 years 16,507,747 13,322,695 435,240 $ 18,350,395 $ 15,578,025 $ 508,920

Equity (Tables)

Equity (Tables)	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Summary of Share Capital	Share capital Ordinary shares December 31 2017 2018 Numbers of shares authorized (in thousands) 10,000,000 5,000,000 Numbers of shares reserved (in thousands) Employee share options 800,000 400,000 Number of shares issued and fully paid (in thousands) 8,738,079 4,321,714 December 31 2017 2018 NT$ NT$ US$ (Note 4) Share capital authorized $ 100,000,000 $ 50,000,000 $ 1,633,453 Share capital reserved Employee share options $ 8,000,000 $ 4,000,000 $ 130,676 Share capital issued and fully paid $ 87,380,787 $ 43,217,144 $ 1,411,864
Summary of Capital Surplus	Capital surplus December 31 2017 2018 NT$ NT$ US$ (Note 4) May be used to offset a deficit, distributed as cash dividends, or transferred to share capital (1) Issuance of ordinary shares $ 21,553,853 $ 12,906,401 $ 421,640 Merger by share exchange - 117,693,658 3,844,942 Conversion of bonds payable 1,930,066 - - Difference between consideration and the carrying amount of the subsidiaries’ net assets during actual disposal or acquisition 7,176,958 6,034,102 197,128 30,660,877 136,634,161 4,463,710 December 31 2017 2018 NT$ NT$ US$ (Note 4) May be used to offset a deficit only Changes in percentage of ownership interest in subsidiaries (2) $ 6,084,895 $ 3,727,336 $ 121,768 Treasury share transactions 1,151,345 182,354 5,957 Exercised employee share options 1,089,178 1,366,480 44,642 Expired share options (Notes 22 and 29) 223,454 645,978 21,103 Share of changes in capital surplus of associates 83,733 87,136 2,847 Dividends that the claim period has elapsed and unclaimed by shareholders - 872 29 8,632,605 6,010,156 196,346 May not be used for any purpose Employee share options 960,888 583,542 19,064 Equity component of convertible bonds 214,022 - - Others (3) 155,936 48,805 1,594 1,330,846 632,347 20,658 $ 40,624,328 $ 143,276,664 $ 4,680,714 1) Such capital surplus may be used to offset a deficit; in addition, when the Company has no deficit, such capital surplus may be distributed as cash dividends or transferred to share capital (limited to a certain percentage of the Company’s capital surplus and once a year). 2) Such capital surplus arises from the effect of changes in ownership interest in a subsidiary resulted from equity transactions other than actual disposal or acquisition, or from changes in capital surplus of subsidiaries accounted for using the equity method. 3) Such capital surplus represents the excess of the carrying amount of related accounts over the par value due to employee share options exercised and the Company has not completed registration formalities.
Summary of Unrealized Gain (Loss) on Financial Assets at FVTOCI	Unrealized gain (loss) on financial assets at FVTOCI For the Year Ended December 31, 2018 NT$ US$ (Note 4) Balance at January 1 per IAS 39 $ 422,570 $ 13,805 Adjustment on initial application of IFRS 9 (Note 3) (287,053 ) (9,377 ) Balance at January 1 per IFRS 9 135,517 4,428 Unrealized gain (loss) recognized during the year Debt instruments (63,076 ) (2,061 ) Equity instruments (398,513 ) (13,019 ) Share from associates and joint venture accounted for using the equity method (555,271 ) (18,140 ) Realized loss (gain) recognized during the year Disposal of equity instruments and transferred cumulative gain to retained earnings (1,518 ) (50 ) Disposal of associates and joint venture accounted for using the equity method (133,364 ) (4,357 ) Share from associates and joint venture accounted for using the equity method 1,118 36 Balance at December 31 $ (1,015,107 ) $ (33,163 )
Summary of Treasury Shares	Treasury shares (in thousand shares) Balance at Balance at January 1 Addition Decrease December 31 2016 Shares held by subsidiaries 145,883 - - 145,883 Shares reserved for bonds conversion 120,000 - - 120,000 265,883 - - 265,883 Balance at Balance at January 1 Addition Decrease December 31 2017 Shares held by subsidiaries 145,883 - - 145,883 Shares reserved for bonds conversion 120,000 - - 120,000 265,883 - - 265,883 2018 Shares held by subsidiaries 145,883 - (72,942 ) 72,941 Shares reserved for bonds conversion 120,000 - (120,000 ) - Shares repurchased from dissenting shareholders in accordance with Business Mergers And Acquisitions Act - 1,852 (1,852 ) - 265,883 1,852 (194,794 ) 72,941
Summary of Shares Held By Subsidiaries	The Company’s shares held by its subsidiaries at each balance sheet date were as follows: Shares Held By Subsidiaries Carrying Amount Carrying Amount Fair Value Fair Value (in thousand NT$ US$ (Note 4) NT$ US$ (Note 4) December 31, 2017 ASE Test 88,200 $ 1,380,721 $ 3,364,848 J&R Holding 46,704 381,709 1,781,749 ASE Test, Inc. 10,979 196,677 418,840 145,883 $ 1,959,107 $ 5,565,437 December 31, 2018 ASE Test 44,100 $ 1,380,721 $ 45,107 $ 2,571,044 $ 83,994 J&R Holding 23,352 381,709 12,470 1,361,415 44,476 ASE Test, Inc. 5,489 196,677 6,425 320,031 10,455 72,941 $ 1,959,107 $ 64,002 $ 4,252,490 $ 138,925
Summary of Non-controlling Interests	Non-controlling interests For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Balance at January 1 $ 11,492,545 $ 12,000,551 $ 13,190,129 $ 430,909 Adjustment on initial application of IFRS 15 (Note 3) - - 5,183 169 Balance at January 1 per IFRS 15 11,492,545 12,000,551 13,195,312 431,078 Share of profit for the year 1,253,438 1,677,941 1,204,217 39,341 Other comprehensive income (loss) Exchange difference on translating foreign operations (601,787 ) (334,920 ) (198,365 ) (6,480 ) Unrealized gain on available-for-sale financial assets 1,129 5,763 - - Unrealized loss on equity instruments at FVTOCI - - (23,928 ) (782 ) Remeasurement on defined benefit plans 8,846 (13,724 ) (30,079 ) (983 ) Non-controlling interests arising from acquisition of subsidiaries (Note 30) - - 3,582,866 117,049 Acquisition of non-controlling interests in subsidiaries 42,857 - (2,492,915 ) (81,441 ) Partial disposal of subsidiaries (Note 32) 26,436 (3,055 ) 1,693,064 55,311 Subsidiaries’ buy back of their own outstanding ordinary shares (Note 32) (912,886 ) - (801,884 ) (26,197 ) For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Non-controlling interest relating to outstanding vested employee share options granted by subsidiaries $ 927,823 $ 263,213 $ 1,936,643 $ 63,268 Non-controlling interest relating to outstanding expired employee share options granted by subsidiaries - (159,200 ) - - Cash dividends to non-controlling interests (237,850 ) (246,440 ) (424,815 ) (13,878 ) Balance at December 31 $ 12,000,551 $ 13,190,129 $ 17,639,487 $ 576,265
Exchange differences on translating foreign operations [member]
Statement [LineItems]
Summary of Other Reserves	Exchange differences on translating foreign operations For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Balance at January 1 $ 4,492,671 $ (1,643,623 ) $ (6,733,659 ) $ (219,982 ) Exchange differences on translating foreign operations (5,843,856 ) (4,952,815 ) 426,186 13,923 Share from associates and joint venture accounted for using the equity method (292,438 ) (137,221 ) 136,608 4,463 Disposal of associates and joint venture accounted for using the equity method - - 282,291 9,222 Balance at December 31 $ (1,643,623 ) $ (6,733,659 ) $ (5,888,574 ) $ (192,374 )
Unrealized gain (loss) on available-for-sale financial assets [member]
Statement [LineItems]
Summary of Other Reserves	Unrealized gain (loss) on available-for-sale financial assets For the Year Ended December 31, 2016 For the Year Ended December 31, 2017 NT$ NT$ Balance at January 1 $ 588,119 $ (197,314 ) Unrealized gain (loss) arising on revaluation of available-for-sale financial assets (257,240 ) 169,585 Cumulative loss reclassified to profit or loss on impairment of available-for-sale financial assets - 50,206 Cumulative loss (gain) reclassified to profit or loss on disposal of available-for-sale financial assets 7,512 (1,517 ) Share from associates and joint venture accounted for using the equity method (535,705 ) 401,610 Balance at December 31 $ (197,314 ) $ 422,570

Profit Before Income Tax (Table

Profit Before Income Tax (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Other Operating Income and Expenses, Net	a. Other operating income and expenses, net For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Rental income $ 51,607 $ 131,570 $ 182,411 $ 5,959 Gains (losses) on disposal of property, plant and equipment and other assets (127,159 ) 367,110 (14,644 ) (479 ) Impairment losses on property, plant and equipment and goodwill (888,231 ) (714,675 ) (133,071 ) (4,347 ) Loss on damages and claims (12,778 ) (85,585 ) (24,114 ) (788 ) Others 176,281 410,136 361,001 11,794 $ (800,280 ) $ 108,556 $ 371,583 $ 12,139
Summary of Other Income	b. Other income For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Government subsidy $ 332,758 $ 341,844 $ 435,950 $ 14,242 Interest income 230,067 306,871 466,211 15,231 Dividends income 26,411 59,039 190,397 6,220 $ 589,236 $ 707,754 $ 1,092,558 $ 35,693
Summary of Other Gains, net	c. Other gains, net For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Gain on remeasurement of investments accounted for using the equity method (Note 15) $ - $ - $ 7,421,408 $ 242,451 Net gains on financial assets mandatorily at FVTPL - - 3,388,485 110,699 Gain on disposal of subsidiaries (Note 31) - 5,589,457 - - Net gains (losses) arising on financial instruments held for trading 224,446 (3,111,253 ) (1,398,995 ) (45,704 ) Net gains on financial assets designated as at FVTPL 223,113 327,351 - - Foreign exchange gains (losses), net 1,928,384 3,502,586 (1,015,615 ) (33,180 ) Impairment losses on financial assets (91,886 ) (50,206 ) (521,010 ) (17,021 ) Others (7,513 ) 1,518 - - $ 2,276,544 $ 6,259,453 $ 7,874,273 $ 257,245
Summary of Finance Costs	d. Finance costs For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Total interest expense for financial liabilities measured at amortized cost $ 2,510,197 $ 2,016,298 $ 3,597,932 $ 117,541 Less: Amounts included in the cost of qualifying assets Inventories related to real estate business (238,469 ) (190,137 ) (11,648 ) (381 ) Property, plant and equipment (54,191 ) (51,262 ) (50,309 ) (1,643 ) Investment properties - (13 ) (89 ) (3 ) 2,217,537 1,774,886 3,535,886 115,514 Other finance costs 43,538 24,608 32,355 1,057 $ 2,261,075 $ 1,799,494 $ 3,568,241 $ 116,571
Summary of Capitalized Borrowing Costs	Information relating to the capitalized borrowing costs was as follows: For the Year Ended December 31 2016 2017 2018 Annual interest capitalization rates Inventories related to real estate business (%) 4.35-6.00 4.35-5.39 4.35 Property, plant and equipment (%) 1.15-4.42 1.26-5.49 1.84-4.52 Investment properties (%) - 1.26-1.97 1.84-2.23
Summary of Depreciation and Amortization	e. Depreciation and amortization For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Property, plant and equipment $ 28,961,614 $ 28,625,287 $ 39,893,786 $ 1,303,293 Investment properties - 122,231 392,667 12,828 Intangible assets 508,823 457,666 2,402,450 78,486 Total $ 29,470,437 $ 29,205,184 $ 42,688,903 $ 1,394,607 Summary of depreciation by function Operating costs $ 26,948,106 $ 26,731,714 $ 37,903,050 $ 1,238,257 Operating expenses 2,013,508 2,015,804 2,383,403 77,864 $ 28,961,614 $ 28,747,518 $ 40,286,453 $ 1,316,121 Summary of amortization by function Operating costs $ 152,987 $ 140,175 $ 1,394,664 $ 45,562 Operating expenses 355,836 317,491 1,007,786 32,924 $ 508,823 $ 457,666 $ 2,402,450 $ 78,486
Summary of Operating Expenses Directly Related to Investment Properties	f. Operating expenses directly related to investment properties For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Direct operating expenses of investment properties that generated rental income $ - $ 465,458 $ 1,276,751 $ 41,710
Summary of Employee Benefits Expense	g. Employee benefits expense For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Post-employment benefits Defined contribution plans $ 2,356,416 $ 2,340,826 $ 2,965,054 $ 96,865 Defined benefit plans 394,741 266,267 291,333 9,518 2,751,157 2,607,093 3,256,387 106,383 Equity-settled share-based payments 470,788 438,765 215,648 7,045 Other employee benefits 49,525,940 51,043,198 63,940,430 2,088,874 $ 52,747,885 $ 54,089,056 $ 67,412,465 $ 2,202,302 Summary of employee benefits expense by function Operating costs $ 35,588,529 $ 35,978,403 $ 45,363,170 $ 1,481,972 Operating expenses 17,159,356 18,110,653 22,049,295 720,330 $ 52,747,885 $ 54,089,056 $ 67,412,465 $ 2,202,302

Income Tax (Tables)

Income Tax (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Major Components of Income Tax Expense	The major components of income tax were as follows: For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Current income tax In respect of the current year $ 4,177,900 $ 4,979,766 $ 5,207,309 $ 170,118 Income tax on unappropriated earnings 829,345 1,076,353 (1,022,560 ) (33,406 ) Changes in estimate for prior years 28,160 (88,162 ) (103,822 ) (3,392 ) 5,035,405 5,967,957 4,080,927 133,320 Deferred income tax In respect of the current year 574,541 534,472 (227,327 ) (7,426 ) Effect of tax rate changes 14,184 - 657,346 21,475 Changes in estimate for prior years (206,788 ) 52,872 5,696 186 Effect of foreign currency exchange differences (26,498 ) (31,698 ) (3,273 ) (107 ) 355,439 555,646 432,442 14,128 Income tax expense recognized in profit or loss $ 5,390,844 $ 6,523,603 $ 4,513,369 $ 147,448
Summary of Reconciliation of Income Tax Expense	A reconciliation of income tax expense calculated at the statutory rates and income tax expense recognized in profit or loss was as follows: For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Profit before income tax $ 27,968,705 $ 31,020,663 $ 31,937,678 $ 1,043,374 Income tax expense calculated at the statutory rates $ 8,634,187 $ 10,890,498 $ 13,540,599 $ 442,359 Nontaxable expense (income) in determining taxable income (34,954 ) 483,715 353,019 11,533 Tax-exempt income (700,274 ) (623,566 ) (2,515,453 ) (82,177 ) Additional income tax on unappropriated earnings 829,345 1,076,353 (1,022,560 ) (33,406 ) For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Loss carry-forward and income tax credits currently used $ (898,700 ) $ (1,124,043 ) $ (971,124 ) $ (31,726 ) Remeasurement of deferred income tax assets, net (2,797,673 ) (4,131,473 ) (4,776,271 ) (156,036 ) Changes in estimate for prior periods 28,160 (88,162 ) (103,822 ) (3,392 ) Withholding tax 81,543 40,281 8,981 293 Land value increment tax 249,210 - - - Income tax expense recognized in profit or loss $ 5,390,844 $ 6,523,603 $ 4,513,369 $ 147,448
Summary of Income Tax Recognized Directly in Equity	b. Income tax recognized directly in equity For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Deferred income tax Related to employee share options $ (204 ) $ 262 $ (1,099 ) $ (36 )
Summary of Income Tax Recognized in Other Comprehensive Income	c. Income tax recognized in other comprehensive income For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Deferred income tax Related to remeasurement of defined benefit plans $ 73,637 $ (51,217 ) $ 55,346 $ 1,808 Effect of tax rate changes - - 70,755 2,312 Income tax recognized in other comprehensive income $ 73,637 $ (51,217 ) $ 126,101 $ 4,120
Summary of Current Tax Assets and Liabilities	d. Current tax assets and liabilities December 31 2017 2018 NT$ NT$ US$ (Note 4) Current tax assets Tax refund receivable $ 28,458 $ 50,456 $ 1,648 Prepaid income tax 232,084 473,807 15,479 $ 260,542 $ 524,263 $ 17,127 Current tax liabilities Income tax payable $ 7,619,328 $ 6,781,136 $ 221,553
Summary of Movements of Deferred Tax Assets and Deferred Tax Liabilities	The movements of deferred tax assets and deferred tax liabilities were as follows: For the year ended December 31, 2016 Balance at January 1 Recognized in Profit or Loss Recognized in Other Comprehensive Income Recognized in Equity Exchange Differences Acquisitions Through Business Combinations Balance at December 31 NT$ NT$ NT$ NT$ NT$ NT$ NT$ Deferred tax assets (liabilities) Temporary differences Property, plant and equipment $ (3,504,458 ) $ (182,291 ) $ - $ - $ (72,098 ) $ - $ (3,758,847 ) Defined benefit obligation 845,939 (48,601 ) 73,637 - 2,509 - 873,484 FVTPL financial instruments (232,198 ) 212,737 - - (1,902 ) - (21,363 ) Others 1,384,987 (283,179 ) - (204 ) (21,780 ) - 1,079,824 (1,505,730 ) (301,334 ) 73,637 (204 ) (93,271 ) - (1,826,902 ) Loss carry-forward 1,323,577 (110,967 ) - - (91,008 ) 2,939 1,124,541 Investment credits 351,119 56,862 - - (25,245 ) - 382,736 $ 168,966 $ (355,439 ) $ 73,637 $ (204 ) $ (209,524 ) $ 2,939 $ (319,625 ) For the year ended December 31, 2017 Balance at January 1 Recognized in Profit or Loss Recognized in Other Comprehensive Income Recognized in Equity Exchange Differences Acquisitions Through Business Combinations Balance at December 31 NT$ NT$ NT$ NT$ NT$ NT$ NT$ Deferred tax assets (liabilities) Temporary differences Property, plant and equipment $ (3,758,847 ) $ (101,576 ) $ - $ - $ (18,643 ) $ - $ (3,879,066 ) Defined benefit obligation 873,484 (26,736 ) (51,217 ) - (15,291 ) - 780,240 FVTPL financial instruments (21,363 ) (86,342 ) - - 2,802 - (104,903 ) Others 1,079,824 (22,748 ) - 262 (28,929 ) - 1,028,409 (1,826,902 ) (237,402 ) (51,217 ) 262 (60,061 ) - (2,175,320 ) Loss carry-forward 1,124,541 (456,246 ) - - 13,146 - 681,441 Investment credits 382,736 138,002 - - 13,475 - 534,213 $ (319,625 ) $ (555,646 ) $ (51,217 ) $ 262 $ (33,440 ) $ - $ (959,666 ) For the year ended December 31, 2018 Balance at January 1 Adjustment on initial Application of IFRS 15 Recognized in Profit or Loss Recognized in Other Comprehensive Income Recognized in Equity Exchange Differences Acquisitions Through Business Combinations Balance at December 31 NT$ NT$ NT$ NT$ NT$ NT$ NT$ NT$ Deferred tax assets (liabilities) Temporary differences Property, plant and equipment $ (3,879,066 ) $ - $ (600,229 ) $ - $ - $ (21,146 ) $ (45,873 ) $ (4,546,314 ) Defined benefit obligation 780,240 - (131,687 ) 126,101 - 27,884 262,286 1,064,824 FVTPL financial instruments (104,903 ) - 284,659 - - (137 ) 27,402 207,021 Others 1,028,409 (97,358 ) (26,147 ) - (1,099 ) 74,327 294,540 1,272,672 (2,175,320 ) (97,358 ) (473,404 ) 126,101 (1,099 ) 80,928 538,355 (2,001,797 ) Loss carry-forward 681,441 - (50,059 ) - - 28,293 12,600 672,275 Investment credits 534,213 - 91,021 - - 5,932 - 631,166 $ (959,666 ) $ (97,358 ) $ (432,442 ) $ 126,101 $ (1,099 ) $ 115,153 $ 550,955 $ (698,356 ) Balance at January 1 Adjustment on initial Application of IFRS 15 Recognized in Profit or Loss Recognized in Other Comprehensive Income Recognized in Equity Exchange Differences Acquisitions Through Business Combinations Balance at December 31 US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) Deferred tax assets (liabilities) Temporary differences Property, plant and equipment $ (126,726 ) $ - $ (19,609 ) $ - $ - $ (691 ) $ (1,499 ) $ (148,525 ) Defined benefit obligation 25,490 - (4,302 ) 4,120 - 911 8,569 34,788 FVTPL financial instruments (3,427 ) - 9,300 - - (4 ) 895 6,764 Others 33,597 (3,181 ) (854 ) - (36 ) 2,428 9,622 41,576 (71,066 ) (3,181 ) (15,465 ) 4,120 (36 ) 2,644 17,587 (65,397 ) Loss carry-forward 22,262 - (1,635 ) - - 924 412 21,963 Investment credits 17,452 - 2,973 - - 194 - 20,619 $ (31,352 ) $ (3,181 ) $ (14,127 ) $ 4,120 $ (36 ) $ 3,762 $ 17,999 $ (22,815 )
Summary of Unrecognized Deferred Tax Assets Related to Loss Carry-forward, Investment Credits and Deductible Temporary Differences	December 31 2017 2018 NT$ NT$ US$ (Note 4) Loss carry-forward $ 542,054 $ 666,043 $ 21,759 Deductible temporary differences 712,141 332,255 10,854 $ 1,254,195 $ 998,298 $ 32,613
Summary of Unused Loss Carry-forward	As of December 31, 2018, the unused loss carry-forward comprised of: Expiry Year NT$ US$ (Note 4) 2019 $ 163,916 $ 5,355 2020 290,460 9,489 Expiry Year NT$ US$ (Note 4) 2021 $ 159,641 $ 5,215 2022 94,287 3,080 2023 and thereafter 630,015 20,582 $ 1,338,319 $ 43,721
Summary of Unused Investment Credits	As of December 31, 2018, unused investment credits comprised of: Remaining Creditable Amount Tax Credit Source NT$ US$ Expiry Year (Note 4) Purchase of machinery and equipment $ 590,694 $ 19,297 2022 Others 40,472 1,322 2023 and thereafter $ 631,166 $ 20,619
Summary of Projects were Exempted From Income Tax	As of December 31, 2018, profits attributable to the following expansion projects were exempted from income tax for a 5-year period: Tax-exemption Period Construction and expansion of 2007 by ASE 2016.01-2020.12 Construction and expansion of 2008 by ASE 2014.01-2018.12 Construction and expansion of 2008 by ASE Test Inc. 2014.01-2018.12 Construction and expansion of 2009 by ASE Test Inc. 2018.01-2022.12 Construction and expansion of 2008 by ASE Electronics Inc. 2016.01-2020.12 Construction and expansion of 2007 by SPIL 2015.01-2019.12

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Earnings and Weighted Average Number of Ordinary Shares Outstanding in Computation of Earnings Per Share	The earnings and weighted average number of ordinary shares outstanding in the computation of earnings per share were as follows: Net profit for the year For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Profit for the year attributable to owners of the Company $ 21,324,423 $ 22,819,119 $ 26,220,721 $ 856,606 Effect of potentially dilutive ordinary shares: From subsidiaries (374,359 ) (813,627 ) (418,295 ) (13,665 ) From the investments in associates (494,388 ) (367,687 ) - - From convertible bonds (1,165,506 ) 93,781 - - Earnings used in the computation of diluted earnings per share $ 19,290,170 $ 21,731,586 $ 25,802,426 $ 842,941 Weighted average number of ordinary shares outstanding For the Year Ended December 31 2016 2017 Before After Before After Retrospectively Retrospectively Retrospectively Retrospectively Adjusted Adjusted Adjusted Adjusted 2018 Weighted average number of ordinary shares in the computation of basic earnings per share 7,662,870 3,831,435 8,160,887 4,080,443 4,245,247 Effect of potentially dilutive ordinary shares: From convertible bonds 515,295 257,648 124,911 62,456 - From employee share options 59,218 29,609 39,868 19,934 5,103 From employees’ compensation 46,746 23,373 43,574 21,787 779 Weighted average number of ordinary shares in computation of diluted earnings per share 8,284,129 4,142,065 8,369,240 4,184,620 4,251,129

Share-based Payment Arrangeme_2

Share-based Payment Arrangements (Tables)	12 Months Ended
	Dec. 31, 2018
ASE Inc. option plans [member]
Statement [LineItems]
Summary of Information About Share Options	Information about share options for the years ended December 31, 2016 and 2017 and for the period from January 1, 2018 to April 29, 2018 was as follows: For the Year Ended December 31 For the Period from January 1, 2018 2016 2017 to April 29, 2018 Weighted Weighted Weighted Average Average Average Number of Exercise Number of Exercise Number of Exercise Options Price Options Price Options Price (In Per Share (In Per Share (In Per Share Thousands) (NT$) Thousands) (NT$) Thousands) (NT$) Balance, beginning of period 252,607 $ 26.6 210,795 $ 27.3 135,961 $ 30.2 Options forfeited (6,056 ) 34.6 (5,407 ) 36.3 (1,692 ) 36.3 Options expired - - (1,790 ) 21.1 - - Options exercised (35,756 ) 20.9 (67,637 ) 21.0 (20,557 ) 26.0 Options transferred to the Company in accordance with the joint share exchange agreement - - - - (113,712 ) 30.9 Balance, end of period 210,795 27.3 135,961 30.2 - - Options exercisable, end of period 123,007 20.8 85,642 26.5 - -
Summary of Outstanding Share Options	Information about the outstanding share options that the Company granted and assumed at each balance sheet date was as follows: Range of Exercise Price Per Share (NT$) Weighted Average Remaining Contractual Life (Years) December 31, 2017 ASE 4 th $ 20.4-22.6 2.5 ASE 5 th 36.5 7.7 December 31, 2018 ASE 4 th 40.8-45.2 1.5 ASE 5 th 73.0 6.7 The Company 1 st 56.4 9.9
ASE Mauritius Inc. option plan [member]
Statement [LineItems]
Summary of Information About Share Options	Information about share options was as follows: For the Year Ended December 31 2016 2017 Number of Exercise Number of Exercise Options Price Options Price (In Per Share (In Per Share Thousands) (US$) Thousands) (US$) Balance at January 1 28,470 $ 1.7 28,470 $ 1.7 Options forfeited - - (250 ) 1.7 Options expired - - (28,220 ) 1.7 Balance at December 31 28,470 1.7 - - Options exercisable, end of year 28,470 1.7 - -
USIE option plans [member]
Statement [LineItems]
Summary of Information About Share Options	Information about share options was as follows: For the Year Ended December 31 2016 2017 2018 Number of Weighted Exercise Number of Weighted Exercise Number of Weighted Exercise Options Price Options Price Options Price (In Per Share (In Per Share (In Per Share Thousands) (US$) Thousands) (US$) Thousands) (US$) Balance at January 1 29,695 $ 2.1 25,933 $ 2.2 25,556 $ 2.2 Options exercised (3,762 ) 2.0 (377 ) 1.9 (8,845 ) 2.2 Balance at December 31 25,933 2.2 25,556 2.2 16,711 2.1 Options exercisable, end of year 25,933 2.2 25,556 2.2 16,711 2.1
Summary of Outstanding Share Options	Information about USIE’s outstanding share options at each balance sheet date was as follows: Range of Exercise Price Per Share (US$) Weighted Average Remaining Contractual Life (Years) December 31, 2017 1 st $ 1.5 3.0 2 nd rd 2.4-2.9 2.9 December 31, 2018 1 st 1.5 2.0 2 nd rd 2.4-2.9 2.1
New shares reserved for subscription by employees under cash capital increase [member]
Statement [LineItems]
Summary of Information About Share Options	Information about ASE’s employee share options related to the aforementioned newly issued shares was as follows: Number of Options (In Thousand) Options granted for the year ended 2017 30,000 Options exercised for the year ended 2017 25,164 Fair value of options granted (NT$ per share) $ 2.80
Summary of Inputs Related to Fair Value of Share Options	Fair value was measured using the Black-Scholes Option Pricing Model and the inputs to the model were as follows: Share price at the grant date NT$36.55 per share Exercise price NT$34.30 per share Expected volatility 27.15% Expected lives 47 days Expected dividend yield - Risk free interest rate 0.37%
Trinomial tree model [member]
Statement [LineItems]
Summary of Inputs Related to Fair Value of Share Options	d. Fair value of share options granted by the Company in 2018 were measured at the grant date by using the trinomial tree model, and the inputs to the model were as follows: Share price at the grant date NT$58.80 per share Exercise price NT$56.40 per share Expected volatility 27.77%-28.86% Expected lives 4.8 years-7.0 years Expected dividend yield - Risk free interest rate 0.73%-0.80%
USISH option plans [member]
Statement [LineItems]
Summary of Information About Share Options	Information about share options was as follows: For the Year Ended December 31 2016 2017 2018 Number of Exercise Number of Exercise Number of Exercise Options Price Options Price Options Price (In Per Share (In Per Share (In Per Share Thousands) (CNY) Thousands) (CNY) Thousands) (CNY) Balance at January 1 26,627 $ 15.5 24,997 $ 15.5 22,341 $ 15.5 Options forfeited (1,630 ) 15.5 (2,656 ) 15.5 (804 ) 15.5 Balance at December 31 24,997 15.5 22,341 15.5 21,537 15.5 Options exercisable, end of year - - 8,896 15.5 12,884 15.5
Joint share exchange agreement [member] | ASE Inc. option plans [member]
Statement [LineItems]
Summary of Information About Share Options	Starting from April 30, 2018, information about the share option plans that the Company granted and assumed was as follows: For the Period from April 30, 2018 to December 31, 2018 Weighted Average Number of Exercise Price Options Per Share (In Thousands) (NT$) Balance, beginning of period - $ - Transferred from ASE 56,856 61.7 Options granted 131,863 56.4 Options forfeited (1,582 ) 71.5 Options exercised (3,323 ) 43.6 Balance, end of period 183,814 58.1 Options exercisable, end of period 36,354 58.1 Fair value of options granted (NT$) $ 16.28-19.12

Business Combinations (Tables)

Business Combinations (Tables)	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Summary of Impact of Acquisitions by Comprehensive Income	As of December 31, 2018, the results of operations from SPIL since the acquisition date were included in the consolidated statements of comprehensive income and were as follows: NT$ US$ (Note 4) Operating revenue $ 61,247,727 $ 2,000,906 Profit $ 7,627,382 $ 249,179
TLJ Intertech Inc. [member]
Statement [LineItems]
Summary of Subsidiary Acquired	a. Subsidiary acquired Principal Activity Date of Acquisition Proportion of Voting Equity Interests Acquired Cash Consideration NT$ TLJ Engaged in information software services May 3, 2016 60 % $ 89,998
Summary of Assets Acquired and Liabilities Assumed at the Date of Acquisition	b. Assets acquired and liabilities assumed at the date of acquisition NT$ Current assets $ 16,645 Non-current assets 108,486 Current liabilities (7,599 ) Fair value of identifiable net assets acquired $ 117,532
Summary of Goodwill Recognized on Acquisition	c. Goodwill recognized on acquisition NT$ Consideration transferred (paid in cash) $ 89,998 Add: Non-controlling interests 42,857 Less: Fair value of identifiable net assets acquired (117,532 ) Goodwill recognized on acquisition $ 15,323
Summary of Net Cash Outflow on Acquisition of Subsidiaries	d. Net cash outflow on acquisition of subsidiaries NT$ Consideration paid in cash $ 89,998 Less: Cash acquired (16,561 ) $ 73,437
Siliconware Precision Industries Co., Ltd. [member]
Statement [LineItems]
Summary of Subsidiary Acquired	a. Subsidiaries acquired Subsidiary Principal Activity Date of Acquisition Proportion of Voting Equity Interests Acquired (%) Consideration Transferred NT$ US$ (Note 4) SPIL Engaged in the assembly, testing and turnkey services of integrated circuits. April 30, 2018 100 % $ 168,440,585 $ 5,502,796
Summary of Assets Acquired and Liabilities Assumed at the Date of Acquisition	b. Assets acquired and liabilities assumed at the date of acquisition NT$ US$ (Note 4) Assets Cash and cash equivalents $ 20,088,970 $ 656,288 Trade and other receivables 15,840,649 517,499 Inventories 5,693,644 186,006 NT$ US$ (Note 4) Property, plant and equipment $ 81,985,622 $ 2,678,393 Intangible assets 31,354,386 1,024,318 Others 24,945,922 814,960 Liabilities Trade and other payables (19,755,598 ) (645,396 ) Borrowings and bonds payables (24,157,174 ) (789,192 ) Others (3,963,201 ) (129,474 ) Fair value of identifiable net assets acquired $ 132,033,220 $ 4,313,402
Summary of Goodwill Recognized on Acquisition	c. Goodwill recognized on acquisitions NT$ US$ (Note 4) Total consideration $ 168,440,585 $ 5,502,796 Add: Non-controlling interests 3,582,866 117,049 Less: Fair value of identifiable net assets acquired (132,033,220 ) (4,313,402 ) Goodwill recognized on acquisition $ 39,990,231 $ 1,306,443
Summary of Net Cash Outflow on Acquisition of Subsidiaries	d. Net cash outflow on acquisition of subsidiaries NT$ US$ (Note 4) Total consideration $ 168,440,585 $ 5,502,796 Less: Payable for consideration representing the ordinary shares originally held by ASE (53,109,760 ) (1,735,046 ) Less: Cash and cash equivalent acquired (20,088,970 ) (656,288 ) $ 95,241,855 $ 3,111,462

Disposal of Subsidiaries (Table

Disposal of Subsidiaries (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Gain on Disposal of Subsidiaries	a. Gain on disposal of subsidiaries NT$ Total consideration $ 7,046,464 Net assets disposed of (1,457,007 ) Gain on disposal of KSDY $ 5,589,457
Summary of Analysis of Assets and Liabilities on Date Control was Lost	b. Analysis of assets and liabilities on the date control was lost NT$ Current assets Cash and cash equivalents $ 29,133 Inventories related to real estate business 1,427,874 Net assets disposed of $ 1,457,007

Cash Flows Information (Tables)

Cash Flows Information (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Non-cash Investing Activities	a. Non-cash investing activities In addition to Notes 22, 25 and 30, the Group entered into the following non-cash investing activities which were not reflected in the consolidated statements of cash flows for the years ended December 31, 2016, 2017 and 2018: For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Payments for property, plant and equipment Purchase of property, plant and equipment $ 27,680,862 $ 23,677,682 $ 39,092,238 $ 1,277,107 For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Increase (decrease) in prepayments for property, plant and equipment $ (89,337 ) $ 90,560 $ 402,255 $ 13,141 Decrease (increase) in payables for property, plant and equipment (823,171 ) 982,260 1,942,259 63,452 Capitalized borrowing costs (54,191 ) (51,262 ) (50,309 ) (1,643 ) $ 26,714,163 $ 24,699,240 $ 41,386,443 $ 1,352,057 Proceeds from disposal of property, plant and equipment Consideration from disposal of property, plant and equipment $ 692,826 $ 1,487,334 $ 1,133,435 $ 37,028 Decrease (increase) in other receivables (22,626 ) 876 (5,791 ) (189 ) $ 670,200 $ 1,488,210 $ 1,127,644 $ 36,839 Payments for investment properties Purchase of investment properties $ - $ 186,535 $ 125,853 $ 4,112 Capitalized borrowing costs - (13 ) (89 ) (3 ) $ - $ 186,522 $ 125,764 $ 4,109 Payments for other intangible assets Purchase of other intangible assets $ 675,144 $ 277,825 $ 537,659 $ 17,565 Decrease (increase) in other payables (120,938 ) 60,159 40,106 1,310 Increase in other non-current liabilities (40,313 ) - - - $ 513,893 $ 337,984 $ 577,765 $ 18,875 Net cash inflow from disposal of subsidiaries Consideration from disposal of subsidiaries $ - $ 7,046,464 $ - $ - Increase in other payables - 3,552 - - Cash and cash equivalents disposed of - (29,133 ) - - $ - $ 7,020,883 $ - $ -
Change in Liabilities Arising From Financing Activities	b. Changes in liabilities arising from financing activities For the year ended December 31, 2017 Short-term borrowings Bonds payable Long-term borrowings Total NT$ NT$ NT$ NT$ Balance at January 1, 2017 $ 20,955,522 $ 36,999,903 $ 53,115,563 $ 111,070,988 Financing cash flows (2,038,993 ) (1,123,972 ) (16,473,381 ) (19,636,346 ) Non-cash changes Bonds conversion - (11,650,369 ) - (11,650,369 ) Amortization of issuance cost - 319,463 5,790 325,253 Effects of exchange rate change (954,058 ) (1,402,245 ) (1,241,344 ) (3,597,647 ) Balance at December 31, 2017 $ 17,962,471 $ 23,142,780 $ 35,406,628 $ 76,511,879 For the year ended December 31, 2018 Short-term borrowings Bonds payable Long-term borrowings Total NT$ NT$ NT$ NT$ Balance at January 1, 2018 $ 17,962,471 $ 23,142,780 $ 35,406,628 $ 76,511,879 Financing cash flows 22,327,813 (6,185,600 ) 85,510,959 101,653,172 Non-cash changes Acquisition through business combinations (Note 30) 3,619,858 4,457,191 16,080,125 24,157,174 Bonds conversion - (4,457,191 ) - (4,457,191 ) Reclassification for applying IFRS 9 (1,301,994 ) - - (1,301,994 ) Amortization of issuance cost - 28,756 188,217 216,973 Effects of foreign currency exchange 655,321 - 712,400 1,367,721 Balance at December 31, 2018 $ 43,263,469 $ 16,985,936 $ 137,898,329 $ 198,147,734 Short-term borrowings Bonds payable Long-term borrowings Total US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) Balance at January 1, 2018 $ 586,817 $ 756,053 $ 1,156,701 $ 2,499,571 Financing cash flows 729,429 (202,078 ) 2,793,563 3,320,914 Non-cash changes Acquisition through business combinations (Note 30) 118,257 145,612 525,323 789,192 Bonds conversion - (145,612 ) - (145,612 ) Reclassification for applying IFRS 9 (42,535 ) - - (42,535 ) Amortization of issuance cost - 940 6,149 7,089 Effects of foreign currency exchange 21,409 - 23,273 44,682 Balance at December 31, 2018 $ 1,413,377 $ 554,915 $ 4,505,009 $ 6,473,301

Operating Lease Arrangements (T

Operating Lease Arrangements (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Future Minimum Lease Payments of Non-cancellable Operating Lease Agreements (Lessee)	The future minimum lease payments of non-cancellable operating lease agreements were as follows: December 31 2017 2018 NT$ NT$ US$ (Note 4) Less than 1 year $ 246,026 $ 509,994 $ 16,661 1-5 years 439,408 828,482 27,066 More than 5 years 419,232 1,047,626 34,225 $ 1,104,666 $ 2,386,102 $ 77,952
Summary of Future Minimum Lease Payments of Non-cancellable Operating Lease Agreements (Lessor)	The future minimum lease payments of non-cancellable operating lease agreements were as follows: December 31, 2018 NT$ US$ (Note 4) Less than 1 year $ 916,891 $ 29,954 1-5 years 2,391,843 78,139 More than 5 years 1,157,093 37,801 $ 4,465,827 $ 145,894

Financial Instruments (Tables)

Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Summary of Categories of Financial Instruments	December 31 2017 2018 NT$ NT$ US$ (Note 4) Financial assets FVTPL Designated as at FVTPL $ 100,496 $ - $ - Held for trading 5,122,571 - - Mandatorily at FVTPL - 7,898,458 258,035 Available-for-sale financial assets 1,212,165 - - Loans and receivables (Note 1) 103,973,567 - - Measured at amortized cost (Note 1) - 139,866,736 4,569,314 FVTOCI Equity instruments - 580,399 18,961 Debt instruments - 1,016,924 33,222 Financial liabilities FVTPL Held for trading 677,430 36,655 1,197 Financial liabilities for hedging - 3,899,634 127,397 Measured at amortized cost (Note 2) 139,561,999 286,035,732 9,344,520 Note 1: The balances included financial assets measured at amortized cost which comprise cash and cash equivalents, trade and other receivables and other financial assets. Note 2: The balances included financial liabilities measured at amortized cost which comprise short-term borrowings, trade and other payables, bonds payable and long-term borrowings.
Summary of Maturity Analysis for Non-derivative Financial Liabilities	On Demand or Less than 1 Month 1 to 3 Months 3 Months to 1 Year 1 to 5 Years More than 5 Years NT$ NT$ NT$ NT$ NT$ December 31, 2017 Non-derivative financial liabilities Non-interest bearing $ 30,695,797 $ 18,387,296 $ 4,549,468 $ 2,807 $ 176,199 Floating interest rate liabilities 6,641,541 4,153,830 5,101,178 27,196,245 900,310 Fixed interest rate liabilities 8,522,765 7,526,270 1,526,449 11,902,335 6,462,396 $ 45,860,103 $ 30,067,396 $ 11,177,095 $ 39,101,387 $ 7,538,905 December 31, 2018 Non-derivative financial liabilities Non-interest bearing $ 33,156,044 $ 34,493,000 $ 6,899,093 $ 57,375 $ 196,523 Floating interest rate liabilities 15,762,004 7,127,606 25,510,718 131,014,040 - Fixed interest rate liabilities 7,677,097 4,811,536 242,461 13,621,814 4,367,546 $ 56,595,145 $ 46,432,142 $ 32,652,272 $ 144,693,229 $ 4,564,069 On Demand or Less than 1 Month 1 to 3 Months 3 Months to 1 Year 1 to 5 Years More than 5 Years US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) December 31, 2018 Non-derivative financial liabilities Non-interest bearing $ 1,083,177 $ 1,126,854 $ 225,387 $ 1,874 $ 6,420 Floating interest rate liabilities 514,930 232,852 833,411 4,280,106 - Fixed interest rate liabilities 250,804 157,188 7,921 445,012 142,684 $ 1,848,911 $ 1,516,894 $ 1,066,719 $ 4,726,992 $ 149,104
Summary of Maturity Analysis for Derivative Financial Instruments	On Demand or Less than 1 Month 1 to 3 Months 3 Months to 1 Year NT$ NT$ NT$ December 31, 2017 Net settled Forward exchange contracts $ (8,820 ) $ - $ - Gross settled Forward exchange contracts Inflows $ 3,711,302 $ 2,169,093 $ 390,379 Outflows (3,679,154 ) (2,138,635 ) (386,880 ) 32,148 30,458 3,499 Swap contracts Inflows 12,116,531 14,434,880 36,676,224 Outflows (12,189,576 ) (14,629,738 ) (36,452,398 ) (73,045 ) (194,858 ) 223,826 $ (40,897 ) $ (164,400 ) $ 227,325 December 31, 2018 Net settled Forward exchange contracts $ 2,040 $ 1,620 $ - Gross settled Forward exchange contracts Inflows $ 2,580,194 $ 466,489 $ - Outflows (2,556,607 ) (460,725 ) - 23,587 5,764 - Swap contracts Inflows Outflows 14,136,620 9,214,500 38,160,316 (13,946,583 ) (8,650,320 ) (36,596,419 ) 190,037 564,180 1,563,897 $ 213,624 $ 569,944 $ 1,563,897 On Demand or Less than 1 Month 1 to 3 Months 3 Months to 1 Year US$ (Note 4) US$ (Note 4) US$ (Note 4) December 31, 2018 Net settled Forward exchange contracts $ 67 $ 53 $ - On Demand or Less than 1 Month 1 to 3 Months 3 Months to 1 Year US$ (Note 4) US$ (Note 4) US$ (Note 4) Gross settled Forward exchange contracts Inflows $ 84,293 $ 15,240 $ - Outflows (83,522 ) (15,052 ) - 771 188 - Swap contracts Inflows 461,830 301,029 1,246,662 Outflows (455,622 ) (282,598 ) (1,195,571 ) 6,208 18,431 51,091 $ 6,979 $ 18,619 $ 51,091
Interest rate risk [member]
Statement [LineItems]
Summary of Interest Rate Risk	The carrying amounts of the Group’s financial assets and financial liabilities with exposure to interest rates at each balance sheet date were as follows: December 31 2017 2018 NT$ NT$ US$ (Note 4) Fair value interest rate risk Financial liabilities $ 17,552,955 $ 17,485,561 $ 571,237 Cash flow interest rate risk Financial assets 39,880,736 32,942,747 1,076,209 Financial liabilities 42,270,321 172,737,393 5,643,169
Level 3 of fair value hierarchy [member]
Statement [LineItems]
Summary of Financial Assets Measured at Level 3 Fair Value	2) Reconciliation of Level 3 fair value measurements of financial assets For the years ended December 31, 2016 and 2017 For the Year Ended December 31 2016 2017 NT$ NT$ Balance at January 1 $ 741,089 $ 904,790 Purchases 495,928 2,649 Total gain or loss In profit or loss (100,734 ) 28 In other comprehensive income (202,565 ) 17,284 Disposals (28,928 ) (16,202 ) Balance at December 31 $ 904,790 $ 908,549 For the year ended December 31, 2018 FVTPL FVTOCI Financial Assets Equity Instruments Equity Instruments Debt Instruments Total NT$ US$ (Note 4) NT$ US$ (Note 4) NT$ US$ (Note 4) NT$ US$ (Note 4) Balance at January 1 (Note 3) $ - $ - $ 908,549 $ 29,681 $ 1,080,000 $ 35,283 $ 1,988,549 $ 64,964 Recognized in profit or loss (2,313 ) (76 ) - - - - (2,313 ) (76 ) Recognized in other comprehensive income (included in unrealized losses on financial assets at FVTOCI) - - (224,172 ) (7,323 ) (63,076 ) (2,061 ) (287,248 ) (9,384 ) Purchases 477,436 15,597 105,000 3,430 - - 582,436 19,027 Disposals - - (208,978 ) (6,827 ) - - (208,978 ) (6,827 ) Balance at December 31 $ 475,123 $ 15,521 $ 580,399 $ 18,961 $ 1,016,924 $ 33,222 $ 2,072,446 $ 67,704
Fair value of financial instruments not measured at fair value but for which fair value is disclosed [member]
Statement [LineItems]
Summary of Fair Value of Financial Instruments	The carrying amounts and fair value of bonds payable as of December 31, 2017 and 2018, respectively, were as follows: Carrying Amount Fair Value NT$ US$ (Note 4) NT$ US$ (Note 4) December 31, 2017 $ 23,142,780 $ 23,247,085 December 31, 2018 16,985,936 $ 554,915 17,126,752 $ 559,515
Measured at fair value on a recurring basis [member]
Statement [LineItems]
Summary of Fair Value of Financial Instruments	1) Fair value hierarchy Level 1 Level 2 Level 3 Total NT$ NT$ NT$ NT$ December 31, 2017 Financial assets at FVTPL Financial assets designated as at FVTPL Private-placement convertible bonds $ - $ 100,496 $ - $ 100,496 Derivative financial assets Forward exchange contracts - 61,325 - 61,325 Swap contracts - 60,538 - 60,538 Non-derivative financial assets held for trading Quoted ordinary shares 4,410,732 - - 4,410,732 Open-end mutual funds 589,976 - - 589,976 $ 5,000,708 $ 222,359 $ - $ 5,223,067 Available-for-sale financial assets Unquoted ordinary shares $ - $ - $ 662,477 $ 662,477 Limited Partnership - - 246,072 246,072 Quoted ordinary shares 279,791 - - 279,791 Open-end mutual funds 23,825 - - 23,825 $ 303,616 $ - $ 908,549 $ 1,212,165 Level 1 Level 2 Level 3 Total NT$ NT$ NT$ NT$ Financial liabilities at FVTPL Derivative financial liabilities Swap contracts $ - $ 652,107 $ - $ 652,107 Forward exchange contracts - 25,323 - 25,323 $ - $ 677,430 $ - $ 677,430 Level 1 Level 2 Level 3 Total NT$ US$ (Note 4) NT$ US$ (Note 4) NT$ US$ (Note 4) NT$ US$ (Note 4) December 31, 2018 Financial assets at FVTPL Derivative financial assets Swap contracts $ - $ - $ 1,557,714 $ 50,889 $ - $ - $ 1,557,714 $ 50,889 Forward exchange contracts - - 32,070 1,048 - - 32,070 1,048 Non-derivative financial assets Quoted ordinary shares 5,151,255 168,287 - - - - 5,151,255 168,287 Open-end mutual funds 581,800 19,007 - - - - 581,800 19,007 Unquoted preferred shares - - - - 275,000 8,984 275,000 8,984 Private-placement funds - - - - 200,123 6,537 200,123 6,537 Hybrid financial assets Private-placement convertible bonds - - 100,496 3,283 - - 100,496 3,283 $ 5,733,055 $ 187,294 $ 1,690,280 $ 55,220 $ 475,123 $ 15,521 $ 7,898,458 $ 258,035 Financial assets at FVTOCI Investments in equity instruments Unquoted shares $ - $ - $ - $ - $ 540,730 $ 17,665 $ 540,730 $ 17,665 Limited partnership - - - - 39,669 1,296 39,669 1,296 Investments in debt instruments Unsecured subordinate corporate bonds - - - - 1,016,924 33,222 1,016,924 33,222 $ - $ - $ - $ - $ 1,597,323 $ 52,183 $ 1,597,323 $ 52,183 Financial liabilities at FVTPL Derivative financial liabilities Swap contracts $ - $ - $ 29,058 $ 949 $ - $ - $ 29,058 $ 949 Forward exchange contracts - - 7,597 248 - - 7,597 248 $ - $ - $ 36,655 $ 1,197 $ - $ - $ 36,655 $ 1,197

Related Party Transactions (Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Compensation to Key Management Personnel	For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Short-term employee benefits $ 790,460 $ 860,631 $ 1,041,216 $ 34,015 Post-employment benefits 4,790 2,858 3,884 127 Share-based payments 11,547 - 9,145 299 $ 806,797 $ 863,489 $ 1,054,245 $ 34,441

Assets Pledged as Collateral _2

Assets Pledged as Collateral or for Security (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Assets Pledged as Collateral or for Security	The following assets were provided as collateral for bank borrowings and the tariff guarantees of imported raw materials: December 31 2017 2018 NT$ NT$ US$ (Note 4) Inventories related to real estate business $ 4,822,043 $ 4,796,126 $ 156,685 Investment properties 7,151,382 6,680,017 218,230 Land use rights (long-term prepayments for lease) 6,813,751 6,515,576 212,858 Other financial assets (including current and non-current) 66,726 496,902 16,233 $ 18,853,902 $ 18,488,621 $ 604,006

Significant Assets and Liabil_2

Significant Assets and Liabilities Denominated in Foreign Currencies (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Significant Assets and Liabilities Denominated in Foreign Currencies	The significant financial assets and liabilities denominated in foreign currencies were as follows: Foreign Currencies (In Thousand) Exchange Rate Carrying Amount (In Thousand) December 31, 2017 Monetary financial assets US$ $ 3,065,296 US$1=NT$29.76 $ 91,223,195 US$ 1,193,369 US$1=CNY6.5342 35,514,653 JPY 5,005,435 JPY1=NT$0.2642 1,322,436 JPY 8,113,284 JPY1=US$0.0089 2,143,530 Monetary financial liabilities US$ 2,902,995 US$1=NT$29.76 86,393,137 US$ 1,007,629 US$1=CNY6.5342 29,987,042 JPY 5,415,677 JPY1=NT$0.2642 1,430,822 JPY 8,598,832 JPY1=US$0.0089 2,271,811 December 31, 2018 Monetary financial assets US$ 3,730,484 US$1=NT$30.715 114,581,814 US$ 1,299,391 US$1=CNY6.8632 39,910,801 JPY 4,412,591 JPY1=NT$0.2782 1,227,583 JPY 6,568,657 JPY1=US$0.0091 1,827,400 Monetary financial liabilities US$ 3,361,523 US$1=NT$30.715 103,249,185 US$ 1,216,654 US$1=CNY6.8632 37,369,521 JPY 7,401,621 JPY1=NT$0.2782 2,059,131 JPY 7,035,704 JPY1=US$0.0091 1,957,333
Summary of Realized and Unrealized Foreign Exchange Gain (Loss)	The significant realized and unrealized foreign exchange gain (loss) were as follows: For the Year Ended December 31 2016 2017 2018 Functional Exchange Rate Net Foreign Exchange Gain Exchange Rate Net Foreign Exchange Gain (Loss) Exchange Rate Net Foreign Exchange Loss NT$ NT$ NT$ US$ (Note 4) NT$ $ 1,494,044 $ 4,130,243 $ (849,234 ) $ (27,744 ) US$ US$1=NT$32.25 203,258 US$1=NT$29.76 (244,802 ) US$1=NT$30.715 (67,476 ) (2,204 ) CNY CNY1=NT$4.649 224,393 CNY1=NT$4.5545 (337,630 ) CNY1=NT$4.4753 (120,005 ) (3,920 ) $ 1,921,695 $ 3,547,811 $ (1,036,715 ) $ ($33,868)

Operating Segments Information

Operating Segments Information (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Segment Information	a. Segment revenues and operation results Adjustments Packaging Testing EMS Others and Eliminations Total NT$ NT$ NT$ NT$ NT$ NT$ For the year ended December 31, 2016 Revenue from external customers $ 125,282,829 $ 27,031,750 $ 115,395,130 $ 7,174,398 $ - $ 274,884,107 Inter-segment revenue (Note 1) 4,929,897 243,980 47,721,424 9,186,359 (62,081,660 ) - Segment revenue 130,212,726 27,275,730 163,116,554 16,360,757 - 336,965,767 Interest income 32,499 41,405 130,659 37,297 (11,793 ) 230,067 Interest expense (1,727,127 ) (5,980 ) (44,433 ) (451,790 ) 11,793 (2,217,537 ) Depreciation and amortization (18,706,891 ) (6,566,936 ) (2,759,298 ) (1,437,312 ) - (29,470,437 ) Share of the profit of associates and joint ventures 1,513,394 (9,484 ) - - - 1,503,910 Impairment loss (974,095 ) (4,136 ) (1,886 ) - - (980,117 ) Segment profit before income tax 13,921,640 7,226,531 4,626,263 2,194,271 - 27,968,705 Expenditures for segment assets 17,561,135 8,247,003 906,042 966,682 - 27,680,862 December 31, 2016 Investments accounted for using the equity method 49,597,195 227,495 - - - 49,824,690 For the year ended December 31, 2017 Revenue from external customers 126,225,119 26,157,277 133,948,016 4,110,796 - 290,441,208 Inter-segment revenue (Note 1) 4,911,026 184,707 47,119,404 8,383,640 (60,598,777 ) - Segment revenue 131,136,145 26,341,984 181,067,420 12,494,436 - 351,039,985 Interest income 43,744 48,532 269,640 214,265 (269,310 ) 306,871 Interest expense (1,969,562 ) (11,920 ) - (62,714 ) 269,310 (1,774,886 ) Depreciation and amortization (19,105,457 ) (6,476,743 ) (2,133,253 ) (1,489,731 ) - (29,205,184 ) Share of the profit or loss of associates and joint ventures 568,291 (42,509 ) - - - 525,782 Impairment loss (218,214 ) (72,798 ) - (473,869 ) - (764,881 ) Segment profit before income tax 12,065,304 6,904,067 6,883,327 5,167,965 - 31,020,663 Expenditures for segment assets 17,769,612 4,507,097 850,235 550,738 - 23,677,682 December 31, 2017 Investments accounted for using the equity method 48,566,333 187,418 - - - 48,753,751 Adjustments Packaging Testing EMS Others and Eliminations Total NT$ NT$ NT$ NT$ NT$ NT$ For the year ended December 31, 2018 Revenue from external customers $ 178,308,222 $ 35,903,202 $ 151,890,384 $ 4,990,613 $ - $ 371,092,421 Inter-segment revenues (Note 1) 3,531,431 212,310 58,836,465 7,637,053 (70,217,259 ) - Segment revenues 181,839,653 36,115,512 210,726,849 12,627,666 - 441,309,680 Interest income 166,761 55,108 354,343 352,232 (462,233 ) 466,211 Interest expense (3,647,601 ) (101,338 ) - (249,180 ) 462,233 (3,535,886 ) Depreciation and amortization (29,491,977 ) (9,560,610 ) (2,065,590 ) (1,570,726 ) - (42,688,903 ) Share of the profit or loss of associates and joint ventures (456,846 ) (23,398 ) - - - (480,244 ) Impairment loss (654,081 ) - - - - (654,081 ) Segment profit before income tax 17,866,431 7,952,484 6,225,984 (107,221 ) - 31,937,678 Expenditures for segment assets 22,787,190 12,991,023 2,529,771 784,254 - 39,092,238 December 31, 2018 Investments accounted for using the equity method 9,152,290 160,018 - - - 9,312,308 Contract assets 3,488,372 1,000,128 - - - 4,488,500 Adjustments Packaging Testing EMS Others and Eliminations Total US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) US$ (Note 4) For the year ended Revenue from external customers $ 5,825,163 $ 1,172,924 $ 4,962,116 $ 163,039 $ - $ 12,123,242 Inter-segment revenues (Note 1) 115,369 6,936 1,922,132 249,495 (2,293,932 ) - Segment revenues 5,940,532 1,179,860 6,884,248 412,534 - 14,417,174 Interest income 5,448 1,801 11,576 11,507 (15,101 ) 15,231 Interest expense (119,164 ) (3,311 ) - (8,140 ) 15,101 (115,514 ) Depreciation and amortization (963,475 ) (312,336 ) (67,481 ) (51,315 ) - (1,394,607 ) Share of the profit or loss of associates and joint ventures (14,925 ) (764 ) - - - (15,689 ) Impairment loss (21,368 ) - - - - (21,368 ) Segment profit before income tax 583,680 259,800 203,397 (3,503 ) - 1,043,374 Expenditures for segment assets 744,436 424,404 82,645 25,621 - 1,277,106 December 31, 2018 Investments accounted for using the equity method 298,996 5,228 - - - 304,224 Contract assets 113,962 32,673 - - - 146,635 Note 1: Inter-segment revenues were eliminated upon consolidation. Note 2: Refer to the table above for information about disaggregation of revenue.
Summary of Revenue from Major Products and Services	b. Revenue from major products and services For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) Packaging service $ 125,282,829 $ 126,225,119 $ 178,308,222 $ 5,825,163 Testing service 27,031,750 26,157,277 35,903,202 1,172,924 Electronic components manufacturing service 115,395,130 133,948,016 151,890,384 4,962,116 Others 7,174,398 4,110,796 4,990,613 163,039 $ 274,884,107 $ 290,441,208 $ 371,092,421 $ 12,123,242
Summary of Geographical Information	1) Net revenues from external customers For the Year Ended December 31 2016 2017 2018 NT$ NT$ NT$ US$ (Note 4) United States $ 180,745,837 $ 196,462,345 $ 230,791,164 $ 7,539,731 Taiwan 38,868,679 35,413,647 45,630,792 1,490,715 Asia 29,896,304 30,201,332 56,031,108 1,830,484 Europe 23,275,732 26,445,240 36,844,258 1,203,668 Others 2,097,555 1,918,644 1,795,099 58,644 $ 274,884,107 $ 290,441,208 $ 371,092,421 $ 12,123,242 2) Non-current assets, excluding financial instruments, post-employment benefit assets and deferred tax assets December 31 2017 2018 NT$ NT$ US$ (Note 4) Taiwan $ 93,350,839 $ 229,944,505 $ 7,512,071 China 45,376,164 59,058,239 1,929,377 Others 25,025,498 25,686,256 839,146 $ 163,752,501 $ 314,689,000 $ 10,280,594

General Information - Additiona

General Information - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018$ / shares
Siliconware Precision Industries Co., Ltd. [member]
Disclosure Of General Information About Financial Statements [line items]
Exchange price per share	$ 51.2

Application of New and Revise_3

Application of New and Revised International Financial Reporting Standards as Issued by the International Accounting Standards Board ("IASB") ( Collectively, "IFRSs") - Summary of Assets and Liablities (Detail) $ in Thousands, $ in Thousands	Jan. 01, 2018USD ($)	Jan. 01, 2018TWD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Jan. 01, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Investments accounted for using the equity method			$ 304,224	$ 9,312,308		$ 48,753,751	$ 49,824,690
FVTPL			$ 258,035	$ 7,898,458		$ 5,223,067
IAS 39 [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Investments accounted for using the equity method	$ 1,592,739				$ 48,753,751
Financial assets	1,763,372				53,976,818
IAS 39 [member] | Mandatorily at fair value through profit or loss [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
FVTPL	170,633				5,223,067
Total fair value through profit or loss	170,633				5,223,067
Reclassifications [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	72,270				2,212,165
Reclassifications [member] | Mandatorily at fair value through profit or loss [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Add: Reclassification from available-for-sale (IAS 39) - required reclassification	9,919	$ 303,616
Total fair value through profit or loss	9,919				303,616
Reclassifications [member] | Financial assets at fair value through other comprehensive income, category [member]
Debt instruments
Add: Reclassification from other financial assets	32,669	1,000,000
Equity instruments
Add: Reclassification from available-for-sale (IAS 39)	29,682	908,549
Total equity and debt instruments measured at fair value through other comprehensive income	62,351	1,908,549
Remeasurements [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Investments accounted for using the equity method	(85)				(2,586)
Financial assets	2,529				77,414
Remeasurements [member] | Financial assets at fair value through other comprehensive income, category [member]
Debt instruments
Add: Reclassification from other financial assets	2,614	80,000
Equity instruments
Total equity and debt instruments measured at fair value through other comprehensive income	2,614	80,000
IFRS9 [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Investments accounted for using the equity method	1,592,655				48,751,165
Financial assets	1,838,170				56,266,397
IFRS9 [member] | Mandatorily at fair value through profit or loss [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Total fair value through profit or loss	180,551				5,526,683
IFRS9 [member] | Financial assets at fair value through other comprehensive income, category [member]
Equity instruments
Total equity and debt instruments measured at fair value through other comprehensive income	64,964	1,988,549
Cash and cash equivalents [member] | IAS 39 [member] | Loans and receivables [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	1,505,327				46,078,066
Cash and cash equivalents [member] | IFRS9 [member] | Amortized cost [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	1,505,327				46,078,066
Derivatives [member] | IAS 39 [member] | Held for trading [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	3,981				121,863
Derivatives [member] | IFRS9 [member] | Mandatorily at fair value through profit or loss [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	3,981				121,863
Equity instruments1 [member] | IAS 39 [member] | Held for trading [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	144,094				4,410,732
Equity instruments1 [member] | IAS 39 [member] | Available-for-sale [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	9,141				279,791
Equity instruments1 [member] | IFRS9 [member] | Mandatorily at fair value through profit or loss [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	144,094				4,410,732
Equity instruments2 [member] | IAS 39 [member] | Available-for-sale [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	29,681				908,549
Equity instruments2 [member] | IFRS9 [member] | Mandatorily at fair value through profit or loss [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	9,141				279,791
Equity instruments2 [member] | IFRS9 [member] | Financial assets measured at fair value through other comprehensive income, category [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	29,681				908,549
Open-end mutual funds [member] | IAS 39 [member] | Held for trading [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	19,274				589,976
Open-end mutual funds [member] | IAS 39 [member] | Available-for-sale [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	778				23,825
Open-end mutual funds [member] | IFRS9 [member] | Mandatorily at fair value through profit or loss [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	19,274				589,976
Debt instruments [member] | IAS 39 [member] | Mandatorily at fair value through profit or loss [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	3,283				100,496
Debt instruments [member] | IAS 39 [member] | Other financial assets [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	32,669				1,000,000
Debt instruments [member] | IFRS9 [member] | Mandatorily at fair value through profit or loss [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	3,283				100,496
Debt instruments [member] | IFRS9 [member] | Financial assets measured at fair value through other comprehensive income, category [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	35,283				1,080,000
Time deposits with original maturity of over three months, pledged time deposits and guarantee deposit [member] | IAS 39 [member] | Loans and receivables [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	13,248				405,520
Time deposits with original maturity of over three months, pledged time deposits and guarantee deposit [member] | IFRS9 [member] | Amortized cost [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	13,248				405,520
Trade receivables and other receivables [member] | IAS 39 [member] | Loans and receivables [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	1,837,722				56,252,661
Trade receivables and other receivables [member] | IFRS9 [member] | Amortized cost [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	1,837,722				56,252,661
Open-end mutual funds [member] | IFRS9 [member] | Mandatorily at fair value through profit or loss [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Financial assets	778				23,825
Retained earnings [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Investments accounted for using the equity method	(5,344)				(163,579)
Financial assets	11,907				364,467
Retained earnings [member] | Mandatorily at fair value through profit or loss [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Add: Reclassification from available-for-sale (IAS 39) - required reclassification	3,615	110,648
Total fair value through profit or loss	3,615				110,648
Retained earnings [member] | Financial assets at fair value through other comprehensive income, category [member]
Equity instruments
Add: Reclassification from available-for-sale (IAS 39)	13,636	417,398
Total equity and debt instruments measured at fair value through other comprehensive income	13,636	417,398
Other equity securities [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Investments accounted for using the equity method	5,259				160,993
Financial assets	(9,378)				(287,053)
Other equity securities [member] | Mandatorily at fair value through profit or loss [member]
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Add: Reclassification from available-for-sale (IAS 39) - required reclassification	(3,615)	(110,648)
Total fair value through profit or loss	(3,615)				$ (110,648)
Other equity securities [member] | Financial assets at fair value through other comprehensive income, category [member]
Debt instruments
Add: Reclassification from other financial assets	2,614	80,000
Equity instruments
Add: Reclassification from available-for-sale (IAS 39)	(13,636)	(417,398)
Total equity and debt instruments measured at fair value through other comprehensive income	$ (11,022)	$ (337,398)

Application of New and Revise_4

Application of New and Revised International Financial Reporting Standards as Issued by the International Accounting Standards Board ("IASB") ( Collectively, "IFRSs") - Schedule of Anticipated Impact on Assets, Liabilities and Equity Of Retrospective Application of the Requirements for the Classification, Measurement and Impairment of Financial Assets (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Jan. 01, 2018USD ($)	Jan. 01, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)	Dec. 31, 2015TWD ($)
Disclosure of expected impact of initial application of new standards or interpretations [line items]
Inventories	$ 1,196,584	$ 36,627,451			$ 24,260,911
Contract assets - current	146,635	4,488,500
Investments accounted for using the equity method	304,224	9,312,308			48,753,751	$ 49,824,690
Deferred tax assets	166,885	5,108,357			4,001,821
Total assets	17,447,301	534,061,927			363,922,272
Current tax liabilities	221,533	6,781,136			7,619,328
Deferred tax liabilities	189,700	5,806,713			4,961,487
Total liabilities	10,291,865	315,034,005			162,612,085
Retained earnings	776,132	23,757,415			73,718,545
NON-CONTROLLING INTERESTS	576,265	17,639,487			13,190,129
Total equity	$ 7,155,436	$ 219,027,922			$ 201,310,187	$ 166,841,165	$ 165,924,980
IAS 18 [member]
Disclosure of expected impact of initial application of new standards or interpretations [line items]
Inventories			$ 792,581	$ 24,260,911
Investments accounted for using the equity method			1,592,739	48,753,751
Deferred tax assets			130,736	4,001,821
Total assets			2,516,056	77,016,483
Current tax liabilities			248,916	7,619,328
Deferred tax liabilities			162,087	4,961,487
Total liabilities			411,003	12,580,815
Retained earnings			2,408,316	73,718,545
NON-CONTROLLING INTERESTS			430,909	13,190,129
Total equity			2,839,225	86,908,674
Adoption of IFRS 15 [member]
Disclosure of expected impact of initial application of new standards or interpretations [line items]
Inventories			747,440	22,879,133
Contract assets - current			64,394	1,971,107
Investments accounted for using the equity method			1,594,050	48,793,890
Deferred tax assets			130,498	3,994,534
Total assets			2,536,382	77,638,664
Current tax liabilities			249,082	7,624,406
Deferred tax liabilities			165,030	5,051,558
Total liabilities			414,112	12,675,964
Retained earnings			2,425,364	74,240,394
NON-CONTROLLING INTERESTS			431,078	13,195,312
Total equity			2,856,442	87,435,706
Adjustments arising from initial application [member]
Disclosure of expected impact of initial application of new standards or interpretations [line items]
Inventories			(45,141)	(1,381,778)
Contract assets - current			64,394	1,971,107
Investments accounted for using the equity method			1,311	40,139
Deferred tax assets			(238)	(7,287)
Total assets			20,326	622,181
Current tax liabilities			166	5,078
Deferred tax liabilities			2,943	90,071
Total liabilities			3,109	95,149
Retained earnings			17,048	521,849
NON-CONTROLLING INTERESTS			169	5,183
Total equity			$ 17,217	$ 527,032

Application of New and Revise_5

Application of New and Revised International Financial Reporting Standards As Issued By The International Accounting Standards Board - Schedule of Differences Between IFRS and IAS 18 Due to Adoption of IAS18 (Detail) $ / shares in Units, $ / shares in Units, $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)$ / shares	Dec. 31, 2018TWD ($)$ / shares	Dec. 31, 2017TWD ($)$ / shares	Dec. 31, 2016TWD ($)$ / shares	Dec. 31, 2018TWD ($)
Disclosure of initial application of standards or interpretations [line items]
Increase in inventories	$ (302,179)	$ (9,249,714)	$ (2,907,848)	$ 3,156,759
Decrease in non-controlling interests	386,156	11,820,227	246,440	3,063,623
Decrease in operating revenues	(12,123,242)	(371,092,421)	(290,441,208)	(274,884,107)
Decrease in operating costs	(10,125,102)	(309,929,371)	(237,708,937)	(221,696,922)
Increase in share of profit of associates and joint ventures	(15,689)	(480,244)	525,782	1,503,910
Decrease in income tax expense	147,448	4,513,369	6,523,603	5,390,844
TOTAL COMPREHENSIVE INCOME FOR THE YEAR	$ 868,071	$ 26,571,677	$ 19,859,127	$ 14,618,602
Decrease in basic earnings per share | (per share)	$ 0.20	$ 6.18	$ 5.59	$ 5.57
Decrease in diluted earnings per share | (per share)	$ 0.20	$ 6.07	$ 5.19	$ 4.66
IAS 18 [member]
Disclosure of initial application of standards or interpretations [line items]
Increase in inventories	$ 75,572	$ 2,313,269
Decrease in contract assets - current	(146,961)	(4,498,500)
Increase in trade receivables	35,066				$ 1,073,368
Decrease in investments accounted for using the equity method	(1,219)				(37,312)
Increase in deferred tax assets	862				26,389
Decrease in assets	(36,680)	(1,122,786)
Decrease in current tax liabilities	(1,536)				(47,028)
Decrease in deferred tax liabilities	(4,637)	(141,934)
Decrease in liabilities	(6,173)	(188,962)
Decrease in retained earnings	(30,490)	(933,310)
Decrease in non-controlling interests	(17)	(514)
Decrease in equity	(30,507)				$ (933,824)
Decrease in operating revenues	(15,523)	(475,155)
Decrease in operating costs	(3,331)	(101,964)
Increase in share of profit of associates and joint ventures	92	2,828
Decrease in income tax expense	(2,676)	(81,908)
Decrease in net profit and total comprehensive income for the year	(13,290)	(406,792)
Increase (decrease) in net profit and total comprehensive income attributable to: Owners of the Company	(13,442)	(411,461)
Non-controlling interests	152	4,669
TOTAL COMPREHENSIVE INCOME FOR THE YEAR	$ (13,290)	$ (406,792)
IAS 18 [member] | New Taiwan Dollar [member]
Disclosure of initial application of standards or interpretations [line items]
Decrease in basic earnings per share		$ (0.10)
Decrease in diluted earnings per share		$ (0.10)
IAS 18 [member] | US Dollar [member]
Disclosure of initial application of standards or interpretations [line items]
Decrease in basic earnings per share	$ 0
Decrease in diluted earnings per share	$ 0

Application of New and Revise_6

Application of New and Revised International Financial Reporting Standards As Issued By The International Accounting Standards Board - Summary of Anticipated Impact on Assets, Liabilities and Equity (Detail) $ in Thousands, $ in Thousands	Jan. 01, 2019USD ($)	Jan. 01, 2019TWD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of expected impact of initial application of new standards or interpretations [line items]
Other financial assets - current			$ 213,638	$ 6,539,467	$ 472,340
Other current assets			123,273	3,773,384	2,482,010
Long-term prepayments for lease			351,677	10,764,835	8,851,330
Property, plant and equipment			7,010,539	214,592,588	135,168,406
Investment properties			252,806	7,738,379	8,119,436
Other financial assets - non-current			34,116	1,044,294	1,170,500
Other intangible assets			1,009,399	30,897,700	1,406,865
Total assets			17,447,301	534,061,927	363,922,272
Other current liabilities			195,497	5,984,156	4,644,566
Other current liabilities - non-current			44,799	1,371,302	1,210,590
Total liabilities			10,291,865	315,034,005	$ 162,612,085
IAS 17 [member]
Disclosure of expected impact of initial application of new standards or interpretations [line items]
Other financial assets - current			213,638	6,539,467
Other current assets			123,273	3,773,384
Long-term prepayments for lease			351,677	10,764,835
Property, plant and equipment			7,010,539	214,592,588
Investment properties			252,806	7,738,379
Other financial assets - non-current			34,116	1,044,294
Other intangible assets			1,009,399	30,897,700
Total assets			8,995,448	275,350,647
Other current liabilities			195,497	5,984,156
Other current liabilities - non-current			44,799	1,371,302
Total liabilities			240,296	7,355,458
Increase (decrease) due to application of IFRS 16 [member]
Disclosure of expected impact of initial application of new standards or interpretations [line items]
Other financial assets - current			(1)	(31)
Other current assets			(12,578)	(385,014)
Long-term prepayments for lease			(351,677)	(10,764,835)
Property, plant and equipment			(9,052)	(277,079)
Right-of-use assets			350,349	10,724,198
Investment properties			215,591	6,599,225
Other financial assets - non-current			(90)	(2,747)
Other intangible assets			(1,949)	(59,667)
Total assets			190,593	5,834,050
Obligation under leases - current			16,010	490,085
Other current liabilities			(560)	(17,144)
Obligation under leases - non-current			182,884	5,598,071
Other current liabilities - non-current			(7,741)	(236,962)
Total liabilities			$ 190,593	$ 5,834,050
Non adjusting event [member] | IFRS 16 [member]
Disclosure of expected impact of initial application of new standards or interpretations [line items]
Other financial assets - current	$ 213,637	$ 6,539,436
Other current assets	110,695	3,388,370
Property, plant and equipment	7,001,487	214,315,509
Right-of-use assets	350,349	10,724,198
Investment properties	468,397	14,337,604
Other financial assets - non-current	34,026	1,041,547
Other intangible assets	1,007,450	30,838,033
Total assets	9,168,041	281,184,697
Obligation under leases - current	16,010	490,085
Other current liabilities	194,937	5,967,012
Obligation under leases - non-current	182,884	5,598,071
Other current liabilities - non-current	37,058	1,134,340
Total liabilities	$ 430,889	$ 13,189,508

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018$ / $
Summary Of Significant Accounting Policies [abstract]
Ownership interest percentage in subsidiary, assumption	100.00%
Convenience exchange rate	0.3061

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Subsidiaries (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Advanced semiconductor engineering inc [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the packaging and testing of semiconductors and EMS
Establishment and Operating Location	Kaohsiung, R.O.C.
Percentage of Ownership (%)	100.00%	100.00%
A.S.E. Holding Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	Bermuda
Percentage of Ownership (%)	100.00%	100.00%
J & R Holding Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	Bermuda
Percentage of Ownership (%)	100.00%	100.00%
Innosource Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	British Virgin Islands
Percentage of Ownership (%)	100.00%	100.00%
Omniquest Industrial Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	British Virgin Islands
Percentage of Ownership (%)	100.00%	100.00%
ASE Marketing & Service Japan Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in marketing and sales services
Establishment and Operating Location	Japan
Percentage of Ownership (%)	100.00%	100.00%
ASE Test, Inc. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the testing of semiconductors
Establishment and Operating Location	Kaohsiung, R.O.C.
Percentage of Ownership (%)	100.00%	100.00%
Luchu development corporation [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the development of real estate properties
Establishment and Operating Location	Taipei, R.O.C.
Percentage of Ownership (%)	86.10%	86.10%
ASE (Shanghai) Inc. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the production of substrates
Establishment and Operating Location	Shanghai, China
Percentage of Ownership (%)	100.00%	100.00%
ASE Corporation [Member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	British Cayman Islands
Percentage of Ownership (%)	100.00%	100.00%
ASE Mauritius Inc. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	Mauritius
Percentage of Ownership (%)	100.00%	100.00%
ASE Labuan Inc. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	Malaysia
Percentage of Ownership (%)	100.00%	100.00%
Shanghai Ding Hui Real Estate Development Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the development, construction and sale of real estate properties
Establishment and Operating Location	Shanghai, China
Percentage of Ownership (%)	100.00%	100.00%
Shanghai Ding Qi Property Management Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the management of real estate properties
Establishment and Operating Location	Shanghai, China
Percentage of Ownership (%)	100.00%	100.00%
Advanced Semiconductor Engineering (HK) Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the trading of substrates
Establishment and Operating Location	Hong Kong
Percentage of Ownership (%)	100.00%	100.00%
Shanghai Ding Wei Real Estate Development Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the development, construction and leasing of real estate properties
Establishment and Operating Location	Shanghai, China
Percentage of Ownership (%)	100.00%	100.00%
Shanghai Ding Yu Real Estate Development Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the development, construction and leasing of real estate properties
Establishment and Operating Location	Shanghai, China
Percentage of Ownership (%)	100.00%	100.00%
Shanghai Ding Fan Department Store Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in department store business
Establishment and Operating Location	Shanghai, China
Percentage of Ownership (%)	100.00%	100.00%
Kun Shan Ding Hong Real Estate Development Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the development, construction and leasing of real estate properties
Establishment and Operating Location	Kun Shan, China
Percentage of Ownership (%)	100.00%	100.00%
Shanghai Ding Xu Property Management Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the management of real estate properties
Establishment and Operating Location	Shanghai, China
Percentage of Ownership (%)	100.00%	100.00%
ASE Electronics Inc. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the production of substrates
Establishment and Operating Location	Kaohsiung, R.O.C.
Percentage of Ownership (%)	100.00%	100.00%
ASE Test Holdings, Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	British Cayman Islands
Percentage of Ownership (%)	100.00%	100.00%
ASE Holdings (Singapore) Pte. Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	Singapore
Percentage of Ownership (%)	100.00%	100.00%
ASE Singapore Pte. Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the packaging and testing of semiconductors
Establishment and Operating Location	Singapore
Percentage of Ownership (%)	100.00%	100.00%
ISE Labs, Inc. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the testing of semiconductors
Establishment and Operating Location	U.S.A.
Percentage of Ownership (%)	100.00%	100.00%
Universal Global Scientific Industrial Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the manufacturing of components of telecomm and cars and provision of related R&D services
Establishment and Operating Location	Nantou, R.O.C.
Percentage of Ownership (%)	74.60%	75.80%
Universal Scientific Industrial De Mexico S.A. De C.V. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the assembling of motherboards and computer components
Establishment and Operating Location	Mexico
Percentage of Ownership (%)	74.60%	75.80%
USI Japan Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the manufacturing and sale of computer peripherals, integrated chip and other related accessories
Establishment and Operating Location	Japan
Percentage of Ownership (%)	74.60%	75.80%
USI Electronics (Shenzhen) Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the design, manufacturing and sale of motherboards and computer peripherals
Establishment and Operating Location	Shenzhen, China
Percentage of Ownership (%)	74.60%	75.80%
Universal Global Electronics Co., Ltd [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in accepting and outsourcing orders as well as sales of electronic components and service of technical advisory, and was established in February 2018
Establishment and Operating Location	Hong Kong
Percentage of Ownership (%)	74.60%
Universal Scientific Industrial Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the manufacturing, processing and sale of computers, computer peripherals and related accessories
Establishment and Operating Location	Nantou, R.O.C.
Percentage of Ownership (%)	74.40%	75.50%
Siliconware Precision Industries Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the assembly, testing and turnkey services of integrated circuits
Establishment and Operating Location	Taichung, R.O.C.
Percentage of Ownership (%)	100.00%
SPIL (B.V.I.) Holding Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in investing activities
Establishment and Operating Location	British Virgin Islands
Percentage of Ownership (%)	100.00%
Siliconware Investment Co Ltd [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in investing activities
Establishment and Operating Location	Taipei, R.O.C.
Percentage of Ownership (%)	100.00%
Siliconware USA, Inc. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in marketing activities
Establishment and Operating Location	U.S.A.
Percentage of Ownership (%)	100.00%
SPIL (Cayman) Holding Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in investing activities
Establishment and Operating Location	British Cayman Islands
Percentage of Ownership (%)	100.00%
Siliconware technology Suzhou limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the packaging and testing of semiconductors
Establishment and Operating Location	Suzhou, China
Percentage of Ownership (%)	70.00%
Siliconware Electronics (Fujian) Co Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the packaging and testing of semiconductors
Establishment and Operating Location	Fujian, China
Percentage of Ownership (%)	100.00%
TLJ Intertech Inc. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in information software services
Establishment and Operating Location	Taipei, R.O.C.
Percentage of Ownership (%)	60.00%	60.00%
MingFung Information Service Corp Ltd [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in information software services, and was established in May 2018.
Establishment and Operating Location	Taipei, R.O.C.
Percentage of Ownership (%)	100.00%
Alto Enterprises Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	British Virgin Islands
Percentage of Ownership (%)	100.00%	100.00%
Super Zone Holdings Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	Hong Kong
Percentage of Ownership (%)	100.00%	100.00%
ASE (Kun Shan) Inc. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the packaging and testing of semiconductors
Establishment and Operating Location	Kun Shan, China
Percentage of Ownership (%)	100.00%	100.00%
ASE Investment (Kun Shan) Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	Kun Shan, China
Percentage of Ownership (%)	100.00%	100.00%
Advanced Semiconductor Engineering (China) Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Will engage in the packaging and testing of semiconductors
Establishment and Operating Location	Shanghai, China
Percentage of Ownership (%)	100.00%	100.00%
ASE Investment (Labuan) Inc. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	Malaysia
Percentage of Ownership (%)	100.00%	100.00%
ASE Test Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	Singapore
Percentage of Ownership (%)	100.00%	100.00%
ASE (Korea) Inc. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the packaging and testing of semiconductors
Establishment and Operating Location	Korea
Percentage of Ownership (%)	100.00%	100.00%
J&R Industrial Inc. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in leasing equipment and investing activity
Establishment and Operating Location	Kaohsiung, R.O.C.
Percentage of Ownership (%)	100.00%	100.00%
ASE Japan Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the packaging and testing of semiconductors
Establishment and Operating Location	Japan
Percentage of Ownership (%)	100.00%	100.00%
ASE (U.S.) Inc. [member]
Disclosure of subsidiaries [Line Items]
Main Business	After-sales service and sales support
Establishment and Operating Location	U.S.A.
Percentage of Ownership (%)	100.00%	100.00%
Global Advanced Packaging Technology Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	British Cayman Islands
Percentage of Ownership (%)	100.00%	100.00%
ASE WeiHai Inc. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the packaging and testing of semiconductors
Establishment and Operating Location	Shandong, China
Percentage of Ownership (%)	100.00%	100.00%
Suzhou ASEN Semiconductors Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the packaging and testing of semiconductors
Establishment and Operating Location	Suzhou, China
Percentage of Ownership (%)	70.00%	60.00%
Anstock Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in financing activity
Establishment and Operating Location	British Cayman Islands
Percentage of Ownership (%)	100.00%	100.00%
Anstock II Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in financing activity
Establishment and Operating Location	British Cayman Islands
Percentage of Ownership (%)	100.00%	100.00%
ASE Electronics (M) Sdn. Bhd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the packaging and testing of semiconductors
Establishment and Operating Location	Malaysia
Percentage of Ownership (%)	100.00%	100.00%
ASE Assembly & Test (Shanghai) Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the packaging and testing of semiconductors
Establishment and Operating Location	Shanghai, China
Percentage of Ownership (%)	100.00%	100.00%
ASE Trading (Shanghai) Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Liquidated in December 2018
Establishment and Operating Location	Shanghai, China
Percentage of Ownership (%)		100.00%
ISE Labs, China. Ltd [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the testing of semiconductors, and was established in October 2018
Establishment and Operating Location	Shanghai, China
Percentage of Ownership (%)	100.00%
Wuxi Tongzhi Microelectronics Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the packaging and testing of semiconductors
Establishment and Operating Location	Wuxi, China
Percentage of Ownership (%)	100.00%	100.00%
USI Global Inc [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in investing activities, and was established in November 2018 and then dissolved in January 2019
Establishment and Operating Location	Nantou, R.O.C.
Percentage of Ownership (%)	100.00%
USI [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in investing activity
Establishment and Operating Location	Nantou, R.O.C.
Percentage of Ownership (%)	100.00%	99.20%
Huntington Holdings International Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	British Virgin Islands
Percentage of Ownership (%)	100.00%	99.20%
Unitech Holdings International Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	British Virgin Islands
Percentage of Ownership (%)	100.00%	99.20%
Real Tech Holdings Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	British Virgin Islands
Percentage of Ownership (%)	100.00%	99.20%
Universal ABIT Holding Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	In the process of liquidation
Establishment and Operating Location	British Cayman Islands
Percentage of Ownership (%)	100.00%	99.20%
Rising Capital Investment Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	British Virgin Islands
Percentage of Ownership (%)	100.00%	99.20%
Rise Accord Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	British Virgin Islands
Percentage of Ownership (%)	100.00%	99.20%
Universal Scientific Industrial (Kunshan) Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the manufacturing and sale of computer assistance system and related peripherals
Establishment and Operating Location	Kun Shan, China
Percentage of Ownership (%)	100.00%	99.20%
USI Enterprise Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the services of investment advisory and warehousing management
Establishment and Operating Location	Hong Kong
Percentage of Ownership (%)	95.40%	96.90%
Universal Scientific Industrial (Shanghai) Co., Ltd [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the designing, manufacturing and sale of electronic components
Establishment and Operating Location	Shanghai, China
Percentage of Ownership (%)	74.60%	75.80%
Universal Global Technology Co., Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Holding company
Establishment and Operating Location	Hong Kong
Percentage of Ownership (%)	74.60%	75.80%
Universal Global Technology (Kunshan) Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the designing and manufacturing of electronic components
Establishment and Operating Location	Kun Shan, China
Percentage of Ownership (%)	74.60%	75.80%
Universal Global Technology (Shanghai) Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the processing and sales of computer and communication peripherals as well as business in import and export of goods and technology
Establishment and Operating Location	Shanghai, China
Percentage of Ownership (%)	74.60%	75.80%
Universal Global Electronics (Shanghai) Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the sale of electronic components and telecommunications equipment
Establishment and Operating Location	Shanghai, China
Percentage of Ownership (%)	74.60%	75.80%
USI America Inc. [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in the manufacturing and processing of motherboards and wireless network communication and provision of related technical service
Establishment and Operating Location	U.S.A.
Percentage of Ownership (%)	74.60%	75.80%
Universal Global Industrial Co., Limited [member]
Disclosure of subsidiaries [Line Items]
Main Business	Engaged in manufacturing, trading and investing activity
Establishment and Operating Location	Hong Kong
Percentage of Ownership (%)	74.60%	75.80%

Cash and Cash Equivalents - Sum

Cash and Cash Equivalents - Summary of Cash and Cash Equivalents (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)	Dec. 31, 2015TWD ($)
Cash and cash equivalents [abstract]
Cash on hand	$ 259	$ 7,940		$ 8,404
Checking accounts and demand deposits	1,056,185	32,329,820		39,697,319
Cash equivalents	626,615	19,180,676		6,372,343
Cash and cash equivalents,total	$ 1,683,059	$ 51,518,436	$ 1,505,327	$ 46,078,066	$ 38,392,524	$ 55,251,181

Financial Instruments at Fair_3

Financial Instruments at Fair Value Through Profit or Loss - Summary of Financial Instruments at Fair Value Through Profit or Loss (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of detailed information about financial instruments [line items]
Financial assets designated as at FVTPL			$ 100,496
Financial assets held for trading			5,122,571
Financial assets mandatorily classified as at FVTPL	$ 258,035	$ 7,898,458
Financial assets at fair value through profit or loss	258,035	7,898,458	5,223,067
Current	237,250	7,262,227	5,223,067
Non-current	20,785	636,231
Financial liabilities held for trading	1,197	36,655	677,430
Private-placement convertible bonds [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets designated as at FVTPL			100,496
Private-placement convertible bonds [member] | Hybrid financial assets [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	3,283	100,496
Quoted ordinary shares [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets held for trading			4,410,732
Quoted ordinary shares [member] | Non derivative financial assets [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	168,287	5,151,255
Open-end mutual funds [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets held for trading			589,976
Open-end mutual funds [member] | Non derivative financial assets [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	19,007	581,800
Forward Exchange Contract [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets held for trading			61,325
Forward Exchange Contract [member] | Derivative financial instruments [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	1,048	32,070
Swap contracts [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets held for trading			60,538
Swap contracts [member] | Derivative financial instruments [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	50,889	1,557,714
Financial liabilities held for trading	949	29,058	652,107
Unquoted preferred shares [member] | Non derivative financial assets [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	8,984	275,000
Private-placement funds [member] | Non derivative financial assets [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	6,537	200,123
Forward exchange contracts [member] | Derivative financial instruments [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities held for trading	$ 248	$ 7,597	$ 25,323

Financial Instruments at Fair_4

Financial Instruments at Fair Value Through Profit or Loss - Summary of Outstanding Contracts Not Accounted for Hedge Accounting (Detail) € in Thousands, ¥ in Thousands, ¥ in Thousands, RM in Thousands, $ in Thousands, $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2018CNY (¥)	Dec. 31, 2018MYR (RM)	Dec. 31, 2018JPY (¥)	Dec. 31, 2018SGD ($)	Dec. 31, 2018EUR (€)	Dec. 31, 2017TWD ($)	Dec. 31, 2017CNY (¥)	Dec. 31, 2017MYR (RM)	Dec. 31, 2017JPY (¥)	Dec. 31, 2017SGD ($)	Dec. 31, 2017EUR (€)
Swap contracts [member] | Sell NT$/buy US$ [member]
Disclosure of detailed information about financial instruments [line items]
Notional Amount	$ 1,687,400	$ 1,782,400	$ 49,570,469						$ 53,136,302
Swap contracts [member] | Sell NT$/buy US$ [member] | Bottom of range [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period	2019-01	2018-01
Swap contracts [member] | Sell NT$/buy US$ [member] | Top of range [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period	2019-12	2018-12
Swap contracts [member] | Sell US$/buy CNY [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period	2019-01	2018-01
Notional Amount	$ 50,292	$ 52,948		¥ 349,800						¥ 349,800
Swap contracts [member] | Sell US$/buy JPY [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period	2019-01
Notional Amount	$ 54,203	$ 70,324				¥ 6,090,000						¥ 7,870,000
Swap contracts [member] | Sell US$/buy JPY [member] | Bottom of range [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period		2018-02
Swap contracts [member] | Sell US$/buy JPY [member] | Top of range [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period		2018-03
Swap contracts [member] | Sell US$/buy NT$ [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period	2019-01	2018-01
Notional Amount	$ 208,800	$ 217,300	6,423,242						6,505,767
Forward exchange contracts [member] | Sell NT$/buy US$ [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period		2018-01
Notional Amount	$ 80,000	$ 80,000	$ 2,453,540						2,389,620
Forward exchange contracts [member] | Sell NT$/buy US$ [member] | Bottom of range [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period	2019-01
Forward exchange contracts [member] | Sell NT$/buy US$ [member] | Top of range [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period	2019-02
Forward exchange contracts [member] | Sell US$/buy CNY [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period	2019-01
Notional Amount	$ 29,000	$ 125,000		¥ 200,108						¥ 828,858
Forward exchange contracts [member] | Sell US$/buy CNY [member] | Bottom of range [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period		2018-01
Forward exchange contracts [member] | Sell US$/buy CNY [member] | Top of range [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period		2018-04
Forward exchange contracts [member] | Sell US$/buy JPY [member]
Disclosure of detailed information about financial instruments [line items]
Notional Amount	$ 37,733	$ 45,517				¥ 4,231,754						¥ 5,111,101
Forward exchange contracts [member] | Sell US$/buy JPY [member] | Bottom of range [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period	2019-01	2018-01
Forward exchange contracts [member] | Sell US$/buy JPY [member] | Top of range [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period	2019-02	2018-02
Forward exchange contracts [member] | Sell US$/buy NT$ [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period		2018-01
Notional Amount		$ 1,000							$ 30,142
Forward exchange contracts [member] | Sell US$/Buy EUR [Member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period	2019-01	2018-01
Notional Amount	$ 4,103	$ 10,674						€ 3,600						€ 9,000
Forward exchange contracts [member] | Sell US$/Buy MYR [Member]
Disclosure of detailed information about financial instruments [line items]
Notional Amount	$ 14,000	$ 15,000			RM 58,430						RM 61,859
Forward exchange contracts [member] | Sell US$/Buy MYR [Member] | Bottom of range [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period	2019-01	2018-01
Forward exchange contracts [member] | Sell US$/Buy MYR [Member] | Top of range [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period	2019-02	2018-03
Forward exchange contracts [member] | Sell US$/Buy SGD [Member]
Disclosure of detailed information about financial instruments [line items]
Notional Amount	$ 13,400	$ 11,300					$ 18,391						$ 15,305
Forward exchange contracts [member] | Sell US$/Buy SGD [Member] | Bottom of range [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period	2019-01	2018-01
Forward exchange contracts [member] | Sell US$/Buy SGD [Member] | Top of range [member]
Disclosure of detailed information about financial instruments [line items]
Maturity Period	2019-02	2018-02

Financial Assets at Fair Valu_3

Financial Assets at Fair Value Through Other Comprehensive Income - Summary of Financial Assets at Fair Value Through Other Comprehensive Income (Detail) - Dec. 31, 2018 $ in Thousands, $ in Thousands	USD ($)	TWD ($)
Financial assets at fair value through other comprehensive income [abstract]
Investments in equity instruments at FVTOCI	$ 18,961	$ 580,399
Investments in debt instruments at FVTOCI	33,222	1,016,924
Total	$ 52,183	$ 1,597,323

Financial Assets at Fair Valu_4

Financial Assets at Fair Value Through Other Comprehensive Income - Summary of Investments in Equity Instruments at Fair Value Through Other Comprehensive Income (Detail) - Dec. 31, 2018 $ in Thousands, $ in Thousands	USD ($)	TWD ($)
Disclosure of fair value of investments in equity instruments designated at fair value through other comprehensive income [line items]
Investments in equity instruments at FVTOCI	$ 18,961	$ 580,399
Unquoted ordinary shares [member]
Disclosure of fair value of investments in equity instruments designated at fair value through other comprehensive income [line items]
Investments in equity instruments at FVTOCI	17,381	532,047
Limited partnership [member]
Disclosure of fair value of investments in equity instruments designated at fair value through other comprehensive income [line items]
Investments in equity instruments at FVTOCI	1,296	39,669
Unquoted preferred shares [member]
Disclosure of fair value of investments in equity instruments designated at fair value through other comprehensive income [line items]
Investments in equity instruments at FVTOCI	$ 284	$ 8,683

Financial Assets at Fair Valu_5

Financial Assets at Fair Value Through Other Comprehensive Income - Summary of Investments in Debt Instruments at Fair Value Through Other Comprehensive Income (Detail) - Dec. 31, 2018 $ in Thousands, $ in Thousands	USD ($)	TWD ($)
Financial assets at fair value through other comprehensive income [line items]
Investments in debt instruments at FVTOCI	$ 33,222	$ 1,016,924
Unsecured subordinate corporate bonds [member]
Financial assets at fair value through other comprehensive income [line items]
Investments in debt instruments at FVTOCI	$ 33,222	$ 1,016,924

Financial Assets at Fair Valu_6

Financial Assets at Fair Value Through Other Comprehensive Income - Additional Information (Detail) Bonds in Thousands, $ in Thousands, $ in Thousands	1 Months Ended
	Jun. 30, 2016TWD ($)Bonds	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Financial assets at fair value through other comprehensive income [line items]
Unsecured subordinate corporate bonds amount		$ 247,754	$ 7,583,761	$ 1,642,840
Unsecured subordinate corporate bonds [member]
Financial assets at fair value through other comprehensive income [line items]
Unsecured subordinate corporate bonds amount | $	$ 1,000,000			$ 1,000,000
Number of bonds acquired | Bonds	1,000
Corporate bonds annual interest rate	3.50%
Effective interest rate		3.20%	3.20%	3.20%

Available-for-sale Financial _3

Available-for-sale Financial Assets - Summary of Available-for-sale Financial Assets (Detail) $ in Thousands	Dec. 31, 2017TWD ($)
Disclosure of financial assets [Line Items]
Available-for-sale financial assets	$ 1,212,165
Current	89,159
Non-current	1,123,006
Unquoted ordinary shares [member]
Disclosure of financial assets [Line Items]
Available-for-sale financial assets	605,110
Quoted ordinary shares [member]
Disclosure of financial assets [Line Items]
Available-for-sale financial assets	279,791
Limited partnership [member]
Disclosure of financial assets [Line Items]
Available-for-sale financial assets	246,072
Unquoted preferred shares [member]
Disclosure of financial assets [Line Items]
Available-for-sale financial assets	57,367
Open-end mutual funds [member]
Disclosure of financial assets [Line Items]
Available-for-sale financial assets	$ 23,825

Trade Receivables, Net - Summar

Trade Receivables, Net - Summary of Trade Receivables, Net (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of financial assets [Line Items]
Trade receivables	$ 2,596,581	$ 79,481,359	$ 55,200,706
Cost [member]
Disclosure of financial assets [Line Items]
Trade receivables	2,601,658	79,636,748	55,265,607
Allowance for doubtful debts [member]
Disclosure of financial assets [Line Items]
Trade receivables	$ 5,077	$ 155,389	$ 64,901

Trade Receivables, Net - Additi

Trade Receivables, Net - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018
Bottom of range [member]
Disclosure of financial assets [Line Items]
Average credit terms	30 days
Top of range [member]
Disclosure of financial assets [Line Items]
Average credit terms	90 days

Trade Receivables, Net - Summ_2

Trade Receivables, Net - Summary of Loss Allowance of Trade Receivables Based on Group's Provision Matrix (Detail) - Trade receivables [member] $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)
Disclosure of provision matrix [line items]
Gross carrying amount	$ 2,601,658	$ 79,636,748
Loss allowance (Lifetime ECL)	(5,077)	(155,389)
Amortized cost	$ 2,596,581	$ 79,481,359
Not past due [member]
Disclosure of provision matrix [line items]
Expected credit loss rate	0.00%	0.00%
Gross carrying amount	$ 2,346,278	$ 71,819,583
Loss allowance (Lifetime ECL)	(233)	(7,119)
Amortized cost	2,346,045	71,812,464
Less than 1 month [member]
Disclosure of provision matrix [line items]
Gross carrying amount	213,585	6,537,819
Loss allowance (Lifetime ECL)	(147)	(4,463)
Amortized cost	$ 213,438	$ 6,533,356
Less than 1 month [member] | Bottom of range [member]
Disclosure of provision matrix [line items]
Expected credit loss rate	0.00%	0.00%
Less than 1 month [member] | Top of range [member]
Disclosure of provision matrix [line items]
Expected credit loss rate	10.00%	10.00%
1 to 3 months [member]
Disclosure of provision matrix [line items]
Gross carrying amount	$ 25,443	$ 778,799
Loss allowance (Lifetime ECL)	(488)	(14,949)
Amortized cost	$ 24,955	$ 763,850
1 to 3 months [member] | Bottom of range [member]
Disclosure of provision matrix [line items]
Expected credit loss rate	0.00%	0.00%
1 to 3 months [member] | Top of range [member]
Disclosure of provision matrix [line items]
Expected credit loss rate	50.00%	50.00%
More than 91 days [member]
Disclosure of provision matrix [line items]
Gross carrying amount	$ 13,254	$ 405,707
Loss allowance (Lifetime ECL)	(1,309)	(40,080)
Amortized cost	$ 11,945	$ 365,627
More than 91 days [member] | Bottom of range [member]
Disclosure of provision matrix [line items]
Expected credit loss rate	1.00%	1.00%
More than 91 days [member] | Top of range [member]
Disclosure of provision matrix [line items]
Expected credit loss rate	100.00%	100.00%
Individually impaired [member]
Disclosure of provision matrix [line items]
Gross carrying amount	$ 3,098	$ 94,840
Loss allowance (Lifetime ECL)	(2,900)	(88,778)
Amortized cost	$ 198	$ 6,062
Individually impaired [member] | Bottom of range [member]
Disclosure of provision matrix [line items]
Expected credit loss rate	0.00%	0.00%
Individually impaired [member] | Top of range [member]
Disclosure of provision matrix [line items]
Expected credit loss rate	100.00%	100.00%

Trade Receivables, Net - Summ_3

Trade Receivables, Net - Summary of Movements of Loss Allowance of Trade Receivables (Detail) - Trade receivables [member] $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Disclosure of financial assets [Line Items]
Beginning balance	$ 2,120	$ 64,901	$ 53,709	$ 82,906
Net remeasurement of loss allowance	4,905	150,128
Acquisition through business combinations	114	3,482
Amounts written off	(1,964)	(60,109)	(34)
Effects of foreign currency exchange differences	(98)	(3,013)	(2,403)	(1,175)
Ending balance	$ 5,077	$ 155,389	$ 64,901	$ 53,709

Trade Receivables, Net - Summ_4

Trade Receivables, Net - Summary of Aging of Receivables Based on Past Due Date (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of financial assets [Line Items]
Trade receivables	$ 2,596,581	$ 79,481,359	$ 55,200,706
Cost [member]
Disclosure of financial assets [Line Items]
Trade receivables	$ 2,601,658	$ 79,636,748	55,265,607
Cost [member] | Not past due [member]
Disclosure of financial assets [Line Items]
Trade receivables			49,599,512
Cost [member] | Less than 1 month [member]
Disclosure of financial assets [Line Items]
Trade receivables			4,986,491
Cost [member] | 1 to 3 months [member]
Disclosure of financial assets [Line Items]
Trade receivables			562,200
Cost [member] | More than 91 days [member]
Disclosure of financial assets [Line Items]
Trade receivables			$ 117,404

Trade Receivables, Net - Summ_5

Trade Receivables, Net - Summary of Aging of Receivables Past Due but Not Impaired (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of financial assets that are either past due or impaired [line items]
Trade receivables	$ 2,596,581	$ 79,481,359	$ 55,200,706
Past due but not impaired [member]
Disclosure of financial assets that are either past due or impaired [line items]
Trade receivables			5,321,203
Past due but not impaired [member] | 1 to 30 days [member]
Disclosure of financial assets that are either past due or impaired [line items]
Trade receivables			4,942,677
Past due but not impaired [member] | 1 to 3 months [member]
Disclosure of financial assets that are either past due or impaired [line items]
Trade receivables			$ 378,526

Trade Receivables, Net - Summ_6

Trade Receivables, Net - Summary of Movement of Allowance for Doubtful Trade Receivables (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Disclosure of financial assets [Line Items]
Impairment losses recognized	$ (3,267)	$ (100,000)
Trade receivables [member]
Disclosure of financial assets [Line Items]
Beginning balance	2,120	64,901	$ 53,709	$ 82,906
Impairment losses recognized			13,629	(28,022)
Amounts written off	(1,964)	(60,109)	(34)
Effect of foreign currency exchange differences	(98)	(3,013)	(2,403)	(1,175)
Ending balance	$ 5,077	155,389	64,901	53,709
Trade receivables [member] | Impaired individually [member]
Disclosure of financial assets [Line Items]
Beginning balance		25,130	16,453	39,046
Impairment losses recognized			9,527	(21,501)
Effect of foreign currency exchange differences			(850)	(1,092)
Ending balance			25,130	16,453
Trade receivables [member] | Impaired collectively [member]
Disclosure of financial assets [Line Items]
Beginning balance		$ 39,771	37,256	43,860
Impairment losses recognized			4,102	(6,521)
Amounts written off			(34)
Effect of foreign currency exchange differences			(1,553)	(83)
Ending balance			$ 39,771	$ 37,256

Inventories - Summary of Invent

Inventories - Summary of Inventories (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Classes of current inventories [abstract]
Finished goods	$ 250,901	$ 7,680,083	$ 6,740,816
Work in process	104,393	3,195,478	3,452,332
Raw materials	759,582	23,250,801	12,625,502
Supplies	61,816	1,892,194	894,196
Raw materials and supplies in transit	19,892	608,895	548,065
Inventories	$ 1,196,584	$ 36,627,451	$ 24,260,911

Inventories - Additional Inform

Inventories - Additional Information (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Classes of current inventories [abstract]
Cost of inventories recognized as operating costs	$ 10,095,421	$ 309,020,850	$ 237,193,286	$ 219,630,270
Write-downs of inventories	$ 32,046	$ 980,927	$ 398,824	$ 451,780

Inventories Related to Real E_3

Inventories Related to Real Estate Business - Summary of Inventories Related to Real Estate Business (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of detailed information about property, plant and equipment [Line Items]
Inventories related to real estate business	$ 328,671	$ 10,060,608	$ 9,819,516
Land and buildings held for sale [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Inventories related to real estate business	677	20,734	25,825
Construction in progress and machinery in transit [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Inventories related to real estate business	269,597	8,252,348	8,106,166
Land held for construction [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Inventories related to real estate business	$ 58,397	$ 1,787,526	$ 1,687,525

Inventories Related to Real E_4

Inventories Related to Real Estate Business - Additional Information (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of detailed information about property, plant and equipment [Line Items]
Investment properties	$ 252,806	$ 7,738,379	$ 8,119,436
Inventories related to real estate business expected to be recovered longer than twelve months	$ 328,671	$ 10,060,608	9,818,869
Reclassified of buildings and land use right under the line item of "inventories related to real estate - construction in progress" [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Investment properties			6,971,372
Long-term prepayments for lease			$ 5,798,449

Other Financial Assets - Summar

Other Financial Assets - Summary of Other Financial Assets (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Jun. 30, 2016TWD ($)
Disclosure of financial assets [Line Items]
Other financial assets	$ 247,754	$ 7,583,761	$ 1,642,840
Current	213,638	6,539,467	472,340
Non-current	34,116	1,044,294	1,170,500
Time deposits with original maturity of over three months [member]
Disclosure of financial assets [Line Items]
Other financial assets	206,490	6,320,669	405,520
Guaranty deposits [member]
Disclosure of financial assets [Line Items]
Other financial assets	25,031	766,190	170,594
Pledged time deposits [member]
Disclosure of financial assets [Line Items]
Other financial assets	16,231	496,847	59,456
Unsecured subordinate corporate bonds [member]
Disclosure of financial assets [Line Items]
Other financial assets			1,000,000	$ 1,000,000
Others [member]
Disclosure of financial assets [Line Items]
Other financial assets	$ 2	$ 55	$ 7,270

Investments Accounted for Usi_3

Investments Accounted for Using the Equity Method - Summary of Investments Accounted for Using the Equity Method (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Investments in subsidiaries, joint ventures and associates [abstract]
Investments in associates	$ 298,328	$ 9,131,814	$ 48,267,237
Investments in joint venture	5,896	180,494	486,514
Investments accounted for using the equity method	$ 304,224	$ 9,312,308	$ 48,753,751	$ 49,824,690

Investments Accounted for Usi_4

Investments Accounted for Using the Equity Method - Summary of Investments in Associates Accounted for Using the Equity Method (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2018TWD ($)
Disclosure of associates and joint ventures [line items]
Investments in associates	$ 298,328	$ 48,267,237	$ 9,131,814
Siliconware Precision Industries Co., Ltd. [member]
Disclosure of associates and joint ventures [line items]
Main Business	Engaged in assembly, testing and turnkey services of integrated circuits
Operating Location	R.O.C.
Percentages of ownership held by the Group		33.29%
Deca Technologies Inc. [member]
Disclosure of associates and joint ventures [line items]
Main Business	Holding company and the group engaged in manufacturing, development and marketing of wafer level packaging and interconnect technology
Operating Location	British Cayman Islands
Percentages of ownership held by the Group	22.04%	22.04%
Hung Ching Development & Construction Co. [member]
Disclosure of associates and joint ventures [line items]
Main Business	Engaged in the development, construction and leasing of real estate properties
Operating Location	R.O.C.
Percentages of ownership held by the Group	26.22%	26.22%
Hung Ching Kwan Co. [member]
Disclosure of associates and joint ventures [line items]
Main Business	Engaged in the leasing of real estate properties
Operating Location	R.O.C.
Percentages of ownership held by the Group	27.31%	27.31%
Advanced Microelectronic Products Inc. [member]
Disclosure of associates and joint ventures [line items]
Main Business	Engaged in integrated circuit
Operating Location	R.O.C.
Percentages of ownership held by the Group	38.76%	38.76%
ChipMos Technologies Inc [member]
Disclosure of associates and joint ventures [line items]
Main Business	Engaged in the packaging and testing of semiconductors
Operating Location	R.O.C.
Percentages of ownership held by the Group	20.47%
Yann Yuan Investment Co., Ltd. [member]
Disclosure of associates and joint ventures [line items]
Main Business	Engaged in investing activities
Operating Location	R.O.C.
Percentages of ownership held by the Group	32.21%
Cost [member]
Disclosure of associates and joint ventures [line items]
Investments in associates	$ 308,134	$ 48,567,386	9,431,963
Cost [member] | Siliconware Precision Industries Co., Ltd. [member]
Disclosure of associates and joint ventures [line items]
Investments in associates		45,210,371
Cost [member] | Deca Technologies Inc. [member]
Disclosure of associates and joint ventures [line items]
Investments in associates	28,302	1,583,124	866,312
Cost [member] | Hung Ching Development & Construction Co. [member]
Disclosure of associates and joint ventures [line items]
Investments in associates	35,780	1,248,711	1,095,233
Cost [member] | Hung Ching Kwan Co. [member]
Disclosure of associates and joint ventures [line items]
Investments in associates	9,663	309,630	295,772
Cost [member] | Advanced Microelectronic Products Inc. [member]
Disclosure of associates and joint ventures [line items]
Investments in associates	6,015	215,550	184,134
Cost [member] | ChipMos Technologies Inc [member]
Disclosure of associates and joint ventures [line items]
Investments in associates	138,451		4,237,982
Cost [member] | Yann Yuan Investment Co., Ltd. [member]
Disclosure of associates and joint ventures [line items]
Investments in associates	89,923		2,752,530
Deferred gain on transfer of land [member]
Disclosure of associates and joint ventures [line items]
Investments in associates	$ 9,806	$ 300,149	$ 300,149

Investments Accounted for Usi_5

Investments Accounted for Using the Equity Method - Additional Information (Detail) $ in Thousands, $ in Thousands	Feb. 28, 2019USD ($)	Feb. 28, 2019TWD ($)	Oct. 31, 2014USD ($)	Oct. 31, 2014TWD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Disclosure of Investments Accounted for Using Equity Method [line Items]
Impairment losses on financial assets					$ 17,021	$ 521,010	$ 50,206	$ 91,886
Siliconware Precision Industries Co., Ltd. [member]
Disclosure of Investments Accounted for Using Equity Method [line Items]
Gain recognized from remeasuring fair value of equity interest before business combination					$ 242,451	$ 7,421,408
Percentage acquisition of shareholding					100.00%	100.00%
Consideration paid in cash for shares			$ 170,434	$ 5,216,985
Percentage of ownership interest in associate							33.29%
ChipMos Technologies Inc [member]
Disclosure of Investments Accounted for Using Equity Method [line Items]
Ordinary shares acquired						$ 19,159
Consideration paid in cash for shares					$ 14,752	$ 451,563
Percentage of ownership interest in associate					20.47%	20.47%
ChipMos Technologies Inc [member] | Bottom of range [member]
Disclosure of Investments Accounted for Using Equity Method [line Items]
Percentage of ownership interest in associate					18.23%	18.23%
ChipMos Technologies Inc [member] | Top of range [member]
Disclosure of Investments Accounted for Using Equity Method [line Items]
Percentage of ownership interest in associate					20.47%	20.47%
Deca Technologies Inc. [member]
Disclosure of Investments Accounted for Using Equity Method [line Items]
Percentage of ownership interest in associate					22.04%	22.04%	22.04%
Assets discount rate					14.10%	14.10%
ASE Embedded Electronics Inc. [member]
Disclosure of Investments Accounted for Using Equity Method [line Items]
Percentage of ownership interest in joint venture					51.00%	51.00%	51.00%
ASE Embedded Electronics Inc. [member] | Major ordinary share transactions [member]
Disclosure of Investments Accounted for Using Equity Method [line Items]
Consideration paid in cash for shares	$ 49,004	$ 1,500,000
ASE Embedded Electronics Inc. [member] | Major ordinary share transactions [member] | Top of range [member]
Disclosure of Investments Accounted for Using Equity Method [line Items]
Ordinary shares acquired		$ 150,000

Investments Accounted for Usi_6

Investments Accounted for Using the Equity Method - Summary of Fair Values of Investments in Associates with Available Published Price Quotation (Detail) - Level 1 of fair value hierarchy [member] $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Siliconware Precision Industries Co., Ltd. [member]
Disclosure of associates and joint ventures [line items]
Fair value of investments in associates with available published price quotation			$ 52,176,190
Hung Ching Development & Construction Co. [member]
Disclosure of associates and joint ventures [line items]
Fair value of investments in associates with available published price quotation	$ 50,222	$ 1,537,307	1,695,156
Advanced Microelectronic Products Inc. [member]
Disclosure of associates and joint ventures [line items]
Fair value of investments in associates with available published price quotation	12,085	369,925	$ 468,572
ChipMos Technologies Inc [member]
Disclosure of associates and joint ventures [line items]
Fair value of investments in associates with available published price quotation	$ 126,970	$ 3,886,561

Investments Accounted for Usi_7

Investments Accounted for Using the Equity Method - Summarized Financial Information (Detail) $ in Thousands, $ in Thousands	4 Months Ended		12 Months Ended
	Apr. 29, 2018USD ($)	Apr. 29, 2018TWD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2015TWD ($)
Disclosure of associates and joint ventures [line items]
Current assets			$ 6,584,738				$ 201,558,875		$ 144,938,272
Non-current assets			10,862,563				332,503,052		218,984,000
Current liabilities			(5,182,361)				(158,632,082)		(108,376,737)
Non-current liabilities			(5,109,504)				(156,401,923)		(54,235,348)
Equity			7,155,436			$ 166,841,165	219,027,922		201,310,187	$ 165,924,980
Goodwill			1,632,618			10,490,309	49,974,446	$ 324,551	9,934,494	10,506,519
Carrying amount			298,328				9,131,814		48,267,237
Operating revenue			12,123,242	$ 371,092,421	$ 290,441,208	274,884,107
Gross profit			1,998,140	61,163,050	52,732,271	53,187,185
Profit before income tax			1,043,374	31,937,678	31,020,663	27,968,705
Net profit			895,926	27,424,309	24,497,060	22,577,861
Other comprehensive income (loss)			(27,855)	(852,632)	(4,637,933)	(7,959,259)
Total comprehensive income			868,071	$ 26,571,677	$ 19,859,127	14,618,602
Cost [member]
Disclosure of associates and joint ventures [line items]
Goodwill			1,711,485			12,479,305	52,388,559	$ 403,418	12,348,607	$ 12,495,515
Carrying amount			$ 308,134				$ 9,431,963		48,567,386
Siliconware Precision Industries Co., Ltd. [member]
Disclosure of associates and joint ventures [line items]
Current assets									49,065,912
Non-current assets									101,693,417
Current liabilities									(26,194,615)
Non-current liabilities									(27,213,266)
Equity									97,351,448
Proportion of the Group's ownership interest in SPIL					33.29%
Net assets attributable to the Group									32,408,297
Goodwill									12,802,074
Operating revenue	$ 854,918	$ 26,169,040			$ 83,554,385	85,111,913
Gross profit	144,446	4,421,493			12,464,792	15,027,247
Profit before income tax	27,706	848,072			4,347,810	7,351,661
Net profit	13,503	413,317			2,822,231	5,484,462
Other comprehensive income (loss)	20,708	633,879			579,057	(2,373,532)
Total comprehensive income	$ 34,211	$ 1,047,196			3,401,288	3,110,930
Cash dividends received from SPIL					$ 1,815,275	$ 3,941,740
Siliconware Precision Industries Co., Ltd. [member] | Cost [member]
Disclosure of associates and joint ventures [line items]
Carrying amount									$ 45,210,371

Investments Accounted for Usi_8

Investments Accounted for Using the Equity Method - Summary of Aggregate Information of Associates that are Not Individually Material (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Disclosure of associates and joint ventures [line items]
Net profit (loss)	$ 895,926	$ 27,424,309	$ 24,497,060	$ 22,577,861
Other comprehensive income (loss)	(27,855)	(852,632)	(4,637,933)	(7,959,259)
Total comprehensive loss	868,071	26,571,677	19,859,127	14,618,602
Associates that are not individually material [member]
Disclosure of associates and joint ventures [line items]
Net profit (loss)	4,820	147,535	(190,532)	(139,366)
Other comprehensive income (loss)	(20,042)	(613,471)	59,676	(115,650)
Total comprehensive loss	$ (15,222)	$ (465,936)	$ (130,856)	$ (255,016)

Investments Accounted for Usi_9

Investments Accounted for Using the Equity Method - Summary of Aggregate Information of the Joint Venture that is Not Individually Material (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Joint venture that is not individually material [member]
Disclosure of joint ventures [line items]
The Group's share of net loss and total comprehensive loss for the year	$ (10,002)	$ (306,156)	$ (184,366)	$ (90,478)

Property, Plant and Equipment -

Property, Plant and Equipment - Summary of Property, Plant and Equipment (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Disclosure of detailed information about property, plant and equipment [Line Items]
Beginning balance		$ 135,168,406
Depreciation expense	$ 1,303,293	39,893,786	$ 28,625,287	$ 28,961,614
Additions	1,277,107	39,092,238	23,677,682	27,680,862
Ending balance	7,010,539	214,592,588	135,168,406
Cost [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Beginning balance	12,098,015	370,320,242	364,012,147	355,233,007
Additions	1,277,106	39,092,238	23,677,682	27,680,862
Disposals	(962,315)	(29,456,450)	(9,896,428)	(7,069,481)
Reclassification	(486)	(14,891)	(474,352)	(175)
Acquisition through business combinations	5,119,954	156,721,779		1,159
Effect of foreign currency exchange differences	(39,230)	(1,200,829)	(6,998,807)	(11,833,225)
Ending balance	17,493,044	535,462,089	370,320,242	364,012,147
Accumulated depreciation, amortisation and impairment [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Beginning balance	7,682,190	235,151,836	220,131,906	205,235,932
Depreciation expense	1,303,292	39,893,786	28,625,287	28,961,614
Impairment losses recognized	4,348	133,071	289,558	888,231
Disposals	(923,428)	(28,266,113)	(8,757,164)	(6,245,611)
Reclassification	(9)	(265)	(199,745)
Acquisition through business combinations	2,441,561	74,736,157		824
Effect of foreign currency exchange differences	(25,449)	(778,971)	(4,938,006)	(8,709,084)
Ending balance	10,482,505	320,869,501	235,151,836	220,131,906
Land [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Beginning balance		3,258,518
Ending balance	332,113	10,165,969	3,258,518
Land [member] | Cost [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Beginning balance	106,453	3,258,518	3,365,013	3,381,300
Reclassification			(35,965)
Acquisition through business combinations	224,776	6,880,400
Effect of foreign currency exchange differences	884	27,051	(70,530)	(16,287)
Ending balance	332,113	10,165,969	3,258,518	3,365,013
Buildings and improvements [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Beginning balance		58,272,864
Ending balance	2,579,678	78,963,937	58,272,864
Buildings and improvements [member] | Cost [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Beginning balance	3,273,046	100,187,928	96,258,175	94,447,932
Additions	4,734	144,898	350,434	22,341
Disposals	(22,124)	(677,206)	(609,294)	(684,698)
Reclassification	176,044	5,388,709	6,483,392	5,110,102
Acquisition through business combinations	1,212,936	37,127,957
Effect of foreign currency exchange differences	(15,168)	(464,275)	(2,294,779)	(2,637,502)
Ending balance	4,629,468	141,708,011	100,187,928	96,258,175
Buildings and improvements [member] | Accumulated depreciation, amortisation and impairment [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Beginning balance	1,369,326	41,915,064	38,229,544	34,646,878
Depreciation expense	206,663	6,325,948	5,156,558	5,114,263
Impairment losses recognized	965	29,531	2,310	620
Disposals	(16,042)	(491,033)	(478,903)	(449,198)
Reclassification	(9)	(265)	(210,080)	(5,123)
Acquisition through business combinations	493,235	15,097,920
Effect of foreign currency exchange differences	(4,348)	(133,091)	(784,365)	(1,077,896)
Ending balance	2,049,790	62,744,074	41,915,064	38,229,544
Machinery and equipment1 [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Beginning balance		66,185,198
Ending balance	3,531,133	108,087,970	66,185,198
Machinery and equipment1 [member] | Cost [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Beginning balance	8,271,741	253,198,003	248,200,756	243,283,607
Additions	6,294	192,673	102,301	94,480
Disposals	(865,511)	(26,493,282)	(8,449,949)	(5,956,179)
Reclassification	1,047,387	32,060,513	18,331,738	19,661,732
Acquisition through business combinations	3,130,025	95,810,062
Effect of foreign currency exchange differences	(30,368)	(929,579)	(4,986,843)	(8,882,884)
Ending balance	11,559,568	353,838,390	253,198,003	248,200,756
Machinery and equipment1 [member] | Accumulated depreciation, amortisation and impairment [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Beginning balance	6,109,533	187,012,805	175,499,994	164,568,298
Depreciation expense	1,037,283	31,751,251	22,722,307	22,983,290
Impairment losses recognized	3,191	97,680	286,880	876,123
Disposals	(839,751)	(25,704,778)	(7,540,654)	(5,544,489)
Reclassification			34,452	9,660
Acquisition through business combinations	1,738,323	53,210,063
Effect of foreign currency exchange differences	(20,144)	(616,601)	(3,990,174)	(7,392,888)
Ending balance	8,028,435	245,750,420	187,012,805	175,499,994
Other equipment [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Beginning balance		1,588,113
Ending balance	211,145	6,463,160	1,588,113
Other equipment [member] | Cost [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Beginning balance	255,213	7,812,080	8,474,661	7,722,408
Additions	2,772	84,860	130,659	470,901
Disposals	(73,540)	(2,251,060)	(763,937)	(159,822)
Reclassification	70,180	2,148,211	174,947	691,276
Acquisition through business combinations	363,351	11,122,171		1,159
Effect of foreign currency exchange differences	(2,551)	(78,095)	(204,250)	(251,261)
Ending balance	615,425	18,838,167	7,812,080	8,474,661
Other equipment [member] | Accumulated depreciation, amortisation and impairment [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Beginning balance	203,331	6,223,967	6,385,080	5,907,414
Depreciation expense	59,346	1,816,587	746,422	864,061
Impairment losses recognized	192	5,860	368	5,564
Disposals	(67,635)	(2,070,302)	(720,319)	(151,875)
Reclassification			(24,117)	(4,537)
Acquisition through business combinations	210,003	6,428,174		824
Effect of foreign currency exchange differences	(957)	(29,279)	(163,467)	(236,371)
Ending balance	404,280	12,375,007	6,223,967	6,385,080
Construction in progress and machinery in transit [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Beginning balance		5,863,713
Ending balance	356,470	10,911,552	5,863,713
Construction in progress and machinery in transit [member] | Cost [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Beginning balance	191,562	5,863,713	7,713,542	6,397,760
Additions	1,263,306	38,669,807	23,094,288	27,093,140
Disposals	(1,140)	(34,902)	(73,248)	(268,782)
Reclassification	(1,294,097)	(39,612,324)	(25,428,464)	(25,463,285)
Acquisition through business combinations	188,866	5,781,189
Effect of foreign currency exchange differences	7,973	244,069	557,595	(45,291)
Ending balance	$ 356,470	$ 10,911,552	5,863,713	7,713,542
Construction in progress and machinery in transit [member] | Accumulated depreciation, amortisation and impairment [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Beginning balance			17,288	113,342
Impairment losses recognized				5,924
Disposals			$ (17,288)	(100,049)
Effect of foreign currency exchange differences				(1,929)
Ending balance				$ 17,288

Property, Plant and Equipment_2

Property, Plant and Equipment - Additional Information (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Accumulated depreciation, amortisation and impairment [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Impairment losses recognized property plant an equipment	$ 4,348	$ 133,071	$ 289,558	$ 888,231

Property, Plant and Equipment_3

Property, Plant and Equipment - Summary of Property, Plant and Equipment Depreciated Useful Lives (Detail)	12 Months Ended
	Dec. 31, 2018
Bottom of range [member] | Main plant buildings [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Property, plant and equipment useful lives	10 years
Bottom of range [member] | Cleanrooms [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Property, plant and equipment useful lives	10 years
Bottom of range [member] | Others [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Property, plant and equipment useful lives	3 years
Bottom of range [member] | Machinery and equipment1 [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Property, plant and equipment useful lives	2 years
Bottom of range [member] | Other equipment [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Property, plant and equipment useful lives	2 years
Top of range [member] | Main plant buildings [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Property, plant and equipment useful lives	55 years
Top of range [member] | Cleanrooms [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Property, plant and equipment useful lives	20 years
Top of range [member] | Others [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Property, plant and equipment useful lives	20 years
Top of range [member] | Machinery and equipment1 [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Property, plant and equipment useful lives	10 years
Top of range [member] | Other equipment [member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Property, plant and equipment useful lives	20 years

Investment Properties - Summary

Investment Properties - Summary of Investment Properties (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of detailed information about investment property [line items]
Beginning balance		$ 8,119,436
Depreciation expenses	$ 12,828	392,667	$ 122,231
Ending balance	252,806	7,738,379	8,119,436
Land [member]
Disclosure of detailed information about investment property [line items]
Beginning balance		35,965
Ending balance	1,175	35,965	35,965
Buildings and improvements [member]
Disclosure of detailed information about investment property [line items]
Beginning balance		8,083,471
Ending balance	251,631	7,702,414	8,083,471
Cost [member]
Disclosure of detailed information about investment property [line items]
Beginning balance	275,817	8,442,750
Additions	4,111	125,853	186,535
Disposals			(342)
Transferred from inventories related to real estate business and property, plant and equipment	487	14,891	8,150,075
Effects of foreign currency exchange differences	(4,500)	(137,739)	106,482
Ending balance	275,915	8,445,755	8,442,750
Cost [member] | Land [member]
Disclosure of detailed information about investment property [line items]
Beginning balance	1,175	35,965
Transferred from inventories related to real estate business and property, plant and equipment			35,965
Ending balance	1,175	35,965	35,965
Cost [member] | Buildings and improvements [member]
Disclosure of detailed information about investment property [line items]
Beginning balance	274,642	8,406,785
Additions	4,111	125,853	186,535
Disposals			(342)
Transferred from inventories related to real estate business and property, plant and equipment	487	14,891	8,114,110
Effects of foreign currency exchange differences	(4,500)	(137,739)	106,482
Ending balance	274,740	8,409,790	8,406,785
Accumulated depreciation, amortisation and impairment [member]
Disclosure of detailed information about investment property [line items]
Beginning balance	10,562	323,314
Depreciation expenses	12,828	392,667	122,231
Disposals			(161)
Transferred from inventories related to real estate business and property, plant and equipment	9	265	199,745
Effects of foreign currency exchange differences	(290)	(8,870)	1,499
Ending balance	23,109	707,376	323,314
Accumulated depreciation, amortisation and impairment [member] | Buildings and improvements [member]
Disclosure of detailed information about investment property [line items]
Beginning balance	10,562	323,314
Depreciation expenses	12,828	392,667	122,231
Disposals			(161)
Transferred from inventories related to real estate business and property, plant and equipment	9	265	199,745
Effects of foreign currency exchange differences	(290)	(8,870)	1,499
Ending balance	$ 23,109	$ 707,376	$ 323,314

Investment Properties - Investm

Investment Properties - Investment Properties Depreciated on a Straight-Line Basis Over Useful Lives (Detail)	12 Months Ended
	Dec. 31, 2018
Bottom of range [member] | Main plant buildings [Member]
Disclosure of detailed information about investment property [line items]
Investment properties are depreciated using the straight-line method over their estimated useful lives	10 years
Bottom of range [member] | Other Investment Properties [Member]
Disclosure of detailed information about investment property [line items]
Investment properties are depreciated using the straight-line method over their estimated useful lives	3 years
Top of range [member] | Main plant buildings [Member]
Disclosure of detailed information about investment property [line items]
Investment properties are depreciated using the straight-line method over their estimated useful lives	40 years
Top of range [member] | Other Investment Properties [Member]
Disclosure of detailed information about investment property [line items]
Investment properties are depreciated using the straight-line method over their estimated useful lives	20 years

Investment Properties - Additio

Investment Properties - Additional Information (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of detailed information about investment property [line items]
Fair value of investment properties	$ 252,806	$ 7,738,379	$ 8,119,436
Level 3 of fair value hierarchy [member] | Fair value [member]
Disclosure of detailed information about investment property [line items]
Fair value of investment properties	$ 384,346	$ 11,764,829	$ 11,560,440

Goodwill - Summary of Goodwill

Goodwill - Summary of Goodwill (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Disclosure of reconciliation of changes in goodwill [line items]
Beginning balance	$ 324,551	$ 9,934,494	$ 10,490,309	$ 10,506,519
Impairment losses recognized			(425,117)
Acquisition through business combinations	1,306,443	39,990,231		15,323
Effect of foreign currency exchange differences	1,624	49,721	(130,698)	(31,533)
Ending balance	1,632,618	49,974,446	9,934,494	10,490,309
Cost [member]
Disclosure of reconciliation of changes in goodwill [line items]
Beginning balance	403,418	12,348,607	12,479,305	12,495,515
Acquisition through business combinations	1,306,443	39,990,231		15,323
Effect of foreign currency exchange differences	1,624	49,721	(130,698)	(31,533)
Ending balance	1,711,485	52,388,559	12,348,607	12,479,305
Accumulated impairment [Member]
Disclosure of reconciliation of changes in goodwill [line items]
Beginning balance	78,867	2,414,113	1,988,996	1,988,996
Impairment losses recognized			425,117
Ending balance	$ 78,867	$ 2,414,113	$ 2,414,113	$ 1,988,996

Goodwill - Summary of Carrying

Goodwill - Summary of Carrying Amounts of Goodwill Allocated to Cash-generating Units (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)	Dec. 31, 2015TWD ($)
Disclosure of information for cash-generating units [line items]
Goodwill	$ 1,632,618	$ 49,974,446	$ 324,551	$ 9,934,494	$ 10,490,309	$ 10,506,519
Packaging segment [member]
Disclosure of information for cash-generating units [line items]
Goodwill	1,167,245	35,729,371		1,362,724
Testing segment [member]
Disclosure of information for cash-generating units [line items]
Goodwill	439,362	13,448,886		7,775,581
All other segments [member]
Disclosure of information for cash-generating units [line items]
Goodwill	$ 26,011	$ 796,189		$ 796,189

Goodwill - Additional Informati

Goodwill - Additional Information (Detail) - TWD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2016
Disclosure of reconciliation of changes in goodwill [line items]
Impairment loss on goodwill	$ 425,117
Bottom of range [member]
Disclosure of reconciliation of changes in goodwill [line items]
Discount rate applied to cash flow projections	8.97%	8.01%	9.09%
Top of range [member]
Disclosure of reconciliation of changes in goodwill [line items]
Discount rate applied to cash flow projections	11.29%	8.57%	10.49%

Other Intangible Assets - Summa

Other Intangible Assets - Summary of Carrying Amounts of Each Class of Other Intangible Assets (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Disclosure of detailed information about intangible assets [line items]
Beginning balance		$ 1,406,865
Additions	$ 17,565	537,659	$ 277,825	$ 675,144
Amortization expense	78,486	2,402,450	457,666	508,823
Ending balance	1,009,399	30,897,700	1,406,865
Cost [member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance	169,563	5,190,328	5,174,700	4,601,416
Additions	17,565	537,659	277,825	675,144
Disposals or derecognization	(3,254)	(99,589)	(212,317)	(122,946)
Reclassification				786
Acquisition through business combinations	1,029,326	31,507,668		105,509
Effect of foreign currency exchange differences	162	4,969	(49,880)	(85,209)
Ending balance	1,213,362	37,141,035	5,190,328	5,174,700
Accumulated depreciation and amortization [Member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance	123,603	3,783,463	3,557,439	3,219,323
Amortization expense	78,485	2,402,450	457,666	508,823
Disposals or derecognization	(3,249)	(99,433)	(196,224)	(101,174)
Reclassification				786
Acquisition through business combinations	5,008	153,282		506
Effect of foreign currency exchange differences	116	3,573	(35,418)	(70,825)
Ending balance	203,963	6,243,335	3,783,463	3,557,439
Customer relationships [Member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance		113,776
Ending balance	338,673	10,366,797	113,776
Customer relationships [Member] | Cost [member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance	29,913	915,636	915,636	915,636
Disposals or derecognization				(41,099)
Acquisition through business combinations	359,359	11,000,000		41,099
Ending balance	389,272	11,915,636	915,636	915,636
Customer relationships [Member] | Accumulated depreciation and amortization [Member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance	26,196	801,860	721,547	641,234
Amortization expense	24,403	746,979	80,313	121,412
Disposals or derecognization				(41,099)
Ending balance	50,599	1,548,839	801,860	721,547
Computer software [Member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance		864,331
Ending balance	37,886	1,159,682	864,331
Computer software [Member] | Cost [member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance	120,433	3,686,452	3,552,229	3,338,360
Additions	17,278	528,883	265,497	372,188
Disposals or derecognization	(3,115)	(95,358)	(83,595)	(80,537)
Acquisition through business combinations	8,980	274,868
Effect of foreign currency exchange differences	202	6,200	(47,679)	(77,782)
Ending balance	143,778	4,401,045	3,686,452	3,552,229
Computer software [Member] | Accumulated depreciation and amortization [Member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance	92,196	2,822,121	2,608,702	2,385,038
Amortization expense	12,203	373,536	316,580	345,836
Disposals or derecognization	(3,110)	(95,202)	(72,481)	(58,765)
Acquisition through business combinations	4,502	137,799
Effect of foreign currency exchange differences	101	3,109	(30,680)	(63,407)
Ending balance	105,892	3,241,363	2,822,121	2,608,702
Patents and acquired specific technology [Member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance		319,402
Ending balance	629,065	19,255,669	319,402
Patents and acquired specific technology [Member] | Cost [member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance	12,724	389,486	514,443	154,082
Additions				301,351
Disposals or derecognization	(8)	(231)	(123,744)	(1,310)
Reclassification				786
Acquisition through business combinations	659,915	20,200,000		64,380
Effect of foreign currency exchange differences	(29)	(899)	(1,213)	(4,846)
Ending balance	672,602	20,588,356	389,486	514,443
Patents and acquired specific technology [Member] | Accumulated depreciation and amortization [Member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance	2,290	70,084	155,216	138,386
Amortization expense	41,271	1,263,309	43,493	24,154
Disposals or derecognization	(8)	(231)	(123,743)	(1,310)
Reclassification				786
Acquisition through business combinations				483
Effect of foreign currency exchange differences	(16)	(475)	(4,882)	(7,283)
Ending balance	43,537	1,332,687	70,084	155,216
Others [Member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance		109,356
Ending balance	3,775	115,552	109,356
Others [Member] | Cost [member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance	6,493	198,754	192,392	193,338
Additions	287	8,776	12,328	1,605
Disposals or derecognization	(131)	(4,000)	(4,978)
Acquisition through business combinations	1,072	32,800		30
Effect of foreign currency exchange differences	(11)	(332)	(988)	(2,581)
Ending balance	7,710	235,998	198,754	192,392
Others [Member] | Accumulated depreciation and amortization [Member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance	2,921	89,398	71,974	54,665
Amortization expense	608	18,626	17,280	17,421
Disposals or derecognization	(131)	(4,000)
Acquisition through business combinations	506	15,483		23
Effect of foreign currency exchange differences	31	939	144	(135)
Ending balance	$ 3,935	$ 120,446	$ 89,398	$ 71,974

Other Intangible Assets - Sum_2

Other Intangible Assets - Summary of Other Intangible Assets Useful Lives (Detail)	12 Months Ended
	Dec. 31, 2018
Customer relationships [Member]
Disclosure of intangible assets with indefinite useful life [line items]
Other intangible assets useful lives	11 years
Bottom of range [member] | Computer software [Member]
Disclosure of intangible assets with indefinite useful life [line items]
Other intangible assets useful lives	2 years
Bottom of range [member] | Patents and acquired specific technology [Member]
Disclosure of intangible assets with indefinite useful life [line items]
Other intangible assets useful lives	5 years
Bottom of range [member] | Others [Member]
Disclosure of intangible assets with indefinite useful life [line items]
Other intangible assets useful lives	5 years
Top of range [member] | Computer software [Member]
Disclosure of intangible assets with indefinite useful life [line items]
Other intangible assets useful lives	10 years
Top of range [member] | Patents and acquired specific technology [Member]
Disclosure of intangible assets with indefinite useful life [line items]
Other intangible assets useful lives	15 years
Top of range [member] | Others [Member]
Disclosure of intangible assets with indefinite useful life [line items]
Other intangible assets useful lives	32 years

Long-term Prepayments for Lea_2

Long-term Prepayments for Lease - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018
Disclosure of finance lease and operating lease by lessee [line items]
Long-term lease expire date	Through 2048 to 2089
Bottom of range [member]
Disclosure of finance lease and operating lease by lessee [line items]
Long-term lease period	30 years
Top of range [member]
Disclosure of finance lease and operating lease by lessee [line items]
Long-term lease period	70 years

Borrowings - Additional Informa

Borrowings - Additional Information (Detail) - Unsecured revolving bank loans [member]	Dec. 31, 2018	Dec. 31, 2017
Bottom of range [member]
Disclosure of detailed information about borrowings [line items]
Annual interest rates	0.76%	0.80%
Top of range [member]
Disclosure of detailed information about borrowings [line items]
Annual interest rates	5.10%	4.79%

Borrowings - Summary of Bank Lo

Borrowings - Summary of Bank Loans (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of detailed information about borrowings [line items]
Less: current portion	$ 352,141	$ 10,779,034	$ 8,261,625
Noncurrent portion	4,152,868	127,119,295	27,145,003
Bank loans [member]
Disclosure of detailed information about borrowings [line items]
Long-term borrowings	4,403,760	134,799,097	33,407,496
Less: current portion	352,141	10,779,034	8,261,625
Noncurrent portion	4,051,619	124,020,063	25,145,871
Bank loans [member] | Cost [member]
Disclosure of detailed information about borrowings [line items]
Long-term borrowings	4,407,944	134,927,180	33,408,696
Bank loans [member] | Cost [member] | Syndicated bank loans [Member]
Disclosure of detailed information about borrowings [line items]
Long-term borrowings	1,796,798	55,000,000	4,761,600
Bank loans [member] | Cost [member] | Other loans [Member]
Disclosure of detailed information about borrowings [line items]
Long-term borrowings	2,467,604	75,533,354	23,941,947
Bank loans [member] | Cost [member] | Mortgage loans [Member]
Disclosure of detailed information about borrowings [line items]
Long-term borrowings	143,542	4,393,826	4,705,149
Bank loans [member] | Net Unamortized Debt Issue Costs [member]
Disclosure of detailed information about borrowings [line items]
Long-term borrowings	$ 4,184	$ 128,083	$ 1,200

Borrowings - Summary of Bank _2

Borrowings - Summary of Bank Loans (Parenthetical) (Detail) - Bank loans [member]	Dec. 31, 2018	Dec. 31, 2017
Syndicated bank loans [Member]
Disclosure of detailed information about borrowings [line items]
Annual interest rates	1.80%
Syndicated bank loans [Member] | Bottom of range [member]
Disclosure of detailed information about borrowings [line items]
Annual interest rates		2.61%
Syndicated bank loans [Member] | Top of range [member]
Disclosure of detailed information about borrowings [line items]
Annual interest rates		2.70%
Other loans [Member] | Bottom of range [member]
Disclosure of detailed information about borrowings [line items]
Annual interest rates	0.75%	0.93%
Other loans [Member] | Top of range [member]
Disclosure of detailed information about borrowings [line items]
Annual interest rates	3.77%	2.10%
Mortgage loans [Member]
Disclosure of detailed information about borrowings [line items]
Annual interest rates	5.39%
Mortgage loans [Member] | Bottom of range [member]
Disclosure of detailed information about borrowings [line items]
Annual interest rates		4.95%
Mortgage loans [Member] | Top of range [member]
Disclosure of detailed information about borrowings [line items]
Annual interest rates		5.39%

Borrowings - Summary of Long-te

Borrowings - Summary of Long-term Bills Payable (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of detailed information about borrowings [line items]
Long-term bills payable	$ 101,249	$ 3,099,232	$ 1,999,132
Unamortized Discounts [member]
Disclosure of detailed information about borrowings [line items]
Long-term bills payable	25	768	868
Longterm Bills Payable [member]
Disclosure of detailed information about borrowings [line items]
Long-term bills payable	101,274	3,100,000	2,000,000
China Bills Finance Corporation [member]
Disclosure of detailed information about borrowings [line items]
Long-term bills payable	32,669	1,000,000	1,000,000
International Bills Finance Corporation [member]
Disclosure of detailed information about borrowings [line items]
Long-term bills payable	32,669	1,000,000	$ 1,000,000
Ta Ching Bills Finance Corporation [member]
Disclosure of detailed information about borrowings [line items]
Long-term bills payable	$ 35,936	$ 1,100,000

Borrowings - Summary of Long-_2

Borrowings - Summary of Long-term Bills Payable (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
China Bills Finance Corporation [member]
Disclosure of detailed information about borrowings [line items]
Annual interest rates	0.99%	0.96%
Borrowings maturity	February 2020
International Bills Finance Corporation [member]
Disclosure of detailed information about borrowings [line items]
Annual interest rates	1.00%	0.96%
Borrowings maturity	March 2020
Ta Ching Bills Finance Corporation [member]
Disclosure of detailed information about borrowings [line items]
Annual interest rates	0.98%
Borrowings maturity	January 2020

Bonds Payable - Summary of Bond

Bonds Payable - Summary of Bonds Payable (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of detailed information about borrowings [line items]
Bonds payable	$ 554,915	$ 16,985,936	$ 23,142,780
Less: current portion			6,161,197
Noncurrent portion	554,915	16,985,936	16,981,583
Cost [member]
Disclosure of detailed information about borrowings [line items]
Bonds payable	555,374	17,000,000	23,185,600
Cost [member] | Repayable at maturity in January 2021 [member]
Disclosure of detailed information about borrowings [line items]
Bonds payable	228,683	7,000,000	7,000,000
Cost [member] | Repayable at maturity in January 2023 [member]
Disclosure of detailed information about borrowings [line items]
Bonds payable	65,338	2,000,000	2,000,000
Cost [member] | Repayable at maturity in January 2022 [member]
Disclosure of detailed information about borrowings [line items]
Bonds payable	120,876	3,700,000	3,700,000
Cost [member] | Repayable at maturity in January 2024 [member]
Disclosure of detailed information about borrowings [line items]
Bonds payable	140,477	4,300,000	4,300,000
Cost [member] | US$200,000 thousand [member]
Disclosure of detailed information about borrowings [line items]
Bonds payable			6,185,600
Discounts on bonds payable [member]
Disclosure of detailed information about borrowings [line items]
Bonds payable	$ 459	$ 14,064	$ 42,820

Bonds Payable - Summary of Bo_2

Bonds Payable - Summary of Bonds Payable (Parenthetical) (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Jul. 31, 2015
Repayable at maturity in January 2021 [member]
Disclosure of detailed information about borrowings [line items]
Interest rate	1.30%	1.30%
Repayable at maturity in January 2023 [member]
Disclosure of detailed information about borrowings [line items]
Interest rate	1.50%	1.50%
Repayable at maturity in January 2022 [member]
Disclosure of detailed information about borrowings [line items]
Interest rate	1.25%	1.25%
Repayable at maturity in January 2024 [member]
Disclosure of detailed information about borrowings [line items]
Interest rate	1.45%	1.45%
US$200,000 thousand [member]
Disclosure of detailed information about borrowings [line items]
Notional Amount	$ 200,000		$ 200,000

Bonds Payable - Additional Info

Bonds Payable - Additional Information (Detail) $ / shares in Units, $ / shares in Units, $ in Thousands, $ in Thousands	1 Months Ended						12 Months Ended
	Sep. 30, 2017USD ($)	Jul. 31, 2015USD ($)	Oct. 31, 2014USD ($)$ / shares	Oct. 31, 2014TWD ($)	Jul. 31, 2014USD ($)	Sep. 30, 2013USD ($)	Dec. 31, 2017TWD ($)$ / shares	Dec. 31, 2018USD ($)	Jul. 31, 2015TWD ($)$ / shares	Oct. 31, 2014TWD ($)$ / shares
Disclosure of detailed information about borrowings [line items]
Arising from equity component of convertible bonds							$ 214,022
Siliconware Precision Industries Co., Ltd. [member]
Disclosure of detailed information about borrowings [line items]
Bonds maturity period			5 years	5 years
Bonds face amount			$ 400,000
Outstanding bond			148,000
Total consideration			$ 170,434	$ 5,216,985
Consideration per share | (per share)			$ 1.67							$ 51.20
Securities transactions tax			0.30%	0.30%
Change in capital surplus			$ 12,692							$ 388,491
Unsecured overseas convertible bonds [member]
Disclosure of detailed information about borrowings [line items]
Bonds face amount						$ 400,000
Bonds maturity period						5 years
Unsecured overseas bonds conversion right exercised	$ 399,600
Early redeemed the outstanding Bonds	$ 400
Unsecured overseas convertible bonds [member] | Bottom of range [member]
Disclosure of detailed information about borrowings [line items]
Unsecured overseas bonds conversion price | $ / shares							$ 27.95
Unsecured overseas convertible bonds [member] | Top of range [member]
Disclosure of detailed information about borrowings [line items]
Unsecured overseas bonds conversion price | $ / shares							$ 28.96
US$200,000 thousand [member]
Disclosure of detailed information about borrowings [line items]
Bonds face amount		$ 200,000						$ 200,000
Bonds maturity period		2 years 9 months
Unsecured overseas bonds fixed exchange rate | $ / shares									$ 30.928
Arising from equity component of convertible bonds									$ 214,022
Secured Overseas Bonds One [member]
Disclosure of detailed information about borrowings [line items]
Bonds face amount					$ 300,000
Bonds maturity period					3 years
Percentage of ownership interest in subsidiary					100.00%
Annual interest rates of bonds					2.125%

Other Payables - Summary of Oth

Other Payables - Summary of Other Payables (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Subclassifications of assets, liabilities and equities [abstract]
Accrued salary and bonus	$ 346,005	$ 10,591,202	$ 7,292,254
Payables for property, plant and equipment	261,210	7,995,634	4,623,268
Accrued employees' compensation and remuneration to directors	99,262	3,038,417	2,568,880
Accrued employee insurance	28,606	875,638	657,176
Accrued utilities	13,953	427,106	417,257
Payables for patents and acquired specific technology (Note 37)	1,882	57,590	93,000
Others	261,950	8,018,295	5,726,052
Other payables	$ 1,012,868	$ 31,003,882	$ 21,377,887

Retirement Benefit Plans - Addi

Retirement Benefit Plans - Additional Information (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)yr	Dec. 31, 2018TWD ($)yr	Dec. 31, 2017TWD ($)yr	Dec. 31, 2016TWD ($)	Dec. 31, 2018TWD ($)
Disclosure of defined benefit plans [line items]
Percentage of monthly pension contributions	6.00%	6.00%	6.00%	6.00%
Pension costs	$ 9,518	$ 291,333	$ 266,267	$ 394,741
Expected contribution to defined benefit plans	15,820	484,247	272,911
Pension plans for executive managers [member]
Disclosure of defined benefit plans [line items]
Pension costs	364	$ 11,137	3,171	$ 6,872
Accrued pension liabilities	$ 10,472		$ 209,637		$ 320,542
Bottom of range [member]
Disclosure of defined benefit plans [line items]
Average duration of the defined benefit obligation	9	9	8
Top of range [member]
Disclosure of defined benefit plans [line items]
Average duration of the defined benefit obligation	15	15	14

Retirement Benefit Plans - Summ

Retirement Benefit Plans - Summary of Defined Benefit Plans Amounts Included in Consolidated Balance Sheets (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)	Dec. 31, 2015TWD ($)
Disclosure of net defined benefit liability (asset) [abstract]
Present value of the defined benefit obligation	$ 336,398	$ 10,297,139		$ 7,910,638
Fair value of the plan assets	(179,423)	(5,492,123)		(4,341,373)
Present value of unfunded defined benefit obligation	156,975	4,805,016	$ 116,604	3,569,265	$ 3,972,517	$ 3,999,947
Recorded under other payables	(614)	(18,791)		(24,638)
Recorded under other current assets	389	11,910		182,421
Net defined benefit liability	$ 156,750	$ 4,798,135		$ 3,727,048

Retirement Benefit Plans - Su_2

Retirement Benefit Plans - Summary of Movements in Net Defined Benefit Liability (Asset) (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance	$ 116,604	$ 3,569,265	$ 3,972,517	$ 3,999,947
Current service cost	7,322	224,126	278,412	329,838
Past service cost and gain on settlements			(68,979)
Net interest expense (income)	1,832	56,070	53,663	58,031
Recognized in profit or loss	9,154	280,196	263,096	387,869
Return on plan assets (excluding amounts included in net interest)	(542)	(16,589)	52,124	54,549
Actuarial loss (gain) arising from changes in financial assumptions	(282)	(8,643)	56,860	156,193
Actuarial loss (gain) arising from experience adjustments	9,882	302,499	(315,090)	200,723
Actuarial loss arising from changes in demographic assumptions	268	8,190	762	5,716
Actuarial gain arising from changes in other assumptions	742	22,723
Recognized in other comprehensive income	10,068	308,180	(205,344)	417,181
Contributions from the employer	(11,899)	(364,237)	(484,790)	(807,232)
Benefits paid from the Group	(9,669)	(295,953)	(96,575)	(36,033)
Business combinations	42,871	1,312,281
Exchange differences on foreign plans	(154)	(4,716)	120,361	10,785
Ending balance	156,975	4,805,016	3,569,265	3,972,517
Defined benefit obligation [member]
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance	258,433	7,910,638	8,389,884	7,973,676
Current service cost	7,322	224,126	278,412	329,838
Past service cost and gain on settlements			(68,979)
Net interest expense (income)	5,841	178,779	157,404	167,111
Recognized in profit or loss	13,163	402,905	366,837	496,949
Actuarial loss (gain) arising from changes in financial assumptions	(282)	(8,643)	56,860	156,193
Actuarial loss (gain) arising from experience adjustments	9,882	302,499	(315,090)	200,723
Actuarial loss arising from changes in demographic assumptions	268	8,190	762	5,716
Actuarial gain arising from changes in other assumptions	742	22,723
Recognized in other comprehensive income	10,610	324,769	(257,468)	362,632
Benefits paid from the pension fund	(17,706)	(541,989)	(690,830)	(308,471)
Benefits paid from the Group	(9,669)	(295,953)	(96,575)	(36,033)
Business combinations	82,418	2,522,805
Liabilities assumed in a business combination				535
Exchange differences on foreign plans	(851)	(26,036)	198,790	(99,404)
Ending balance	336,398	10,297,139	7,910,638	8,389,884
Fair value of plan assets [member]
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance	(141,829)	(4,341,373)	(4,417,367)	(3,973,729)
Net interest expense (income)	(4,009)	(122,709)	(103,741)	(109,080)
Recognized in profit or loss	(4,009)	(122,709)	(103,741)	(109,080)
Return on plan assets (excluding amounts included in net interest)	(542)	(16,589)	52,124	54,549
Recognized in other comprehensive income	(542)	(16,589)	52,124	54,549
Contributions from the employer	(11,899)	(364,237)	(484,790)	(807,232)
Benefits paid from the pension fund	17,706	541,989	690,830	308,471
Business combinations	(39,547)	(1,210,524)
Liabilities assumed in a business combination				(535)
Exchange differences on foreign plans	697	21,320	(78,429)	110,189
Ending balance	$ (179,423)	$ (5,492,123)	$ (4,341,373)	$ (4,417,367)

Retirement Benefit Plans - Su_3

Retirement Benefit Plans - Summary of Fair Value of the Plan Assets by Major Categories (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of fair value of plan assets [abstract]
Cash	$ 76,475	$ 2,340,903	$ 2,317,764
Debt instruments	29,497	902,886	691,619
Equity instruments	70,725	2,164,895	1,254,109
Others	2,726	83,439	77,881
Total	$ 179,423	$ 5,492,123	$ 4,341,373

Retirement Benefit Plans - Su_4

Retirement Benefit Plans - Summary of Key Assumptions Used for the Actuarial Valuations (Detail)	Dec. 31, 2018	Dec. 31, 2017
Bottom of range [member]
Disclosure of defined benefit plans [line items]
Discount rates	0.05%	0.06%
Expected rates of salary increase	1.75%	2.00%
Top of range [member]
Disclosure of defined benefit plans [line items]
Discount rates	3.02%	3.85%
Expected rates of salary increase	4.06%	4.42%

Retirement Benefit Plans - Su_5

Retirement Benefit Plans - Summary of Sensitivity Analysis on Defined Obligations (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Actuarial assumption of discount rates [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in defined obligation due to increase in actuarial assumption	$ (18,137)	$ (555,181)	$ (455,158)
Change in defined obligation due to decrease in actuarial assumption	19,702	603,089	461,891
Actuarial assumption of expected rates of salary increases [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in defined obligation due to increase in actuarial assumption	19,331	591,712	453,792
Change in defined obligation due to decrease in actuarial assumption	$ (17,887)	$ (547,522)	$ (444,493)

Retirement Benefit Plans - Su_6

Retirement Benefit Plans - Summary of Sensitivity Analysis on Defined Obligations (Parenthetical) (Detail)	Dec. 31, 2018	Dec. 31, 2017
Actuarial assumption of discount rates [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage increase in actuarial assumption	0.50%	0.50%
Percentage decrease in actuarial assumption	0.50%	0.50%
Actuarial assumption of expected rates of salary increases [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage increase in actuarial assumption	0.50%	0.50%
Percentage decrease in actuarial assumption	0.50%	0.50%

Retirement Benefit Plans - Su_7

Retirement Benefit Plans - Summary of Maturity Analysis of Undiscounted Pension Benefit (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of defined benefit plans [line items]
Maturity analysis of undiscounted pension benefit	$ 508,920	$ 15,578,025	$ 18,350,395
Less than 1 year [member]
Disclosure of defined benefit plans [line items]
Maturity analysis of undiscounted pension benefit	12,042	368,592	291,152
1-5 years [member]
Disclosure of defined benefit plans [line items]
Maturity analysis of undiscounted pension benefit	61,638	1,886,738	1,551,496
More than 5 years [member]
Disclosure of defined benefit plans [line items]
Maturity analysis of undiscounted pension benefit	$ 435,240	$ 13,322,695	$ 16,507,747

Equity - Summary of Share Capit

Equity - Summary of Share Capital (Detail) shares in Thousands, $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)shares	Dec. 31, 2018TWD ($)shares	Dec. 31, 2017TWD ($)shares
Disclosure of classes of share capital [abstract]
Numbers of shares authorized (in thousands)	5,000,000	5,000,000	10,000,000
Numbers of shares reserved (in thousands) Employee share options	400,000	400,000	800,000
Number of shares issued and fully paid (in thousands)	4,321,714	4,321,714	8,738,079
Share capital authorized	$ 1,633,453	$ 50,000,000	$ 100,000,000
Share capital reserved Employee share options	130,676	4,000,000	8,000,000
Share capital issued and fully paid	$ 1,411,864	$ 43,217,144	$ 87,380,787

Equity - Additional Information

Equity - Additional Information (Detail) $ / shares in Units, $ in Thousands, $ in Thousands	1 Months Ended		12 Months Ended
	Jun. 30, 2018USD ($)	Jun. 30, 2018TWD ($)	Dec. 31, 2018$ / sharesshares	Dec. 31, 2017shares	Oct. 13, 2017shares	Jul. 13, 2017shares
Disclosure of classes of share capital [line items]
Share price | $ / shares			$ 10
Shares included in authorized shares not yet completed share registration process				500,000,000
Number of ordinary shares issued					323,094,000	101,164,000
Number of shares represented by each ADS			2	2
Distribution of cash from capital surplus arising from issuance of ordinary shares	$ 352,695	$ 10,795,980
Percentage of legal reserve			10.00%
Percentage of legal reserve on share capital			25.00%
American depository shares (ADs) [member]
Disclosure of classes of share capital [line items]
Number of shares represented by each ADS			2
Number of shares outstanding			140,042,000	115,261,000
Ordinary shares [member]
Disclosure of classes of share capital [line items]
Number of shares outstanding			280,085,000	576,305,000
Cash capital increase [member]
Disclosure of classes of share capital [line items]
Share price | $ / shares			$ 34.3
Number of ordinary shares issued			300,000,000
A.S.E. Holding Limited [member]
Disclosure of classes of share capital [line items]
Proportion of ownership interest in subsidiary			100.00%	100.00%
Number of ordinary shares exchanged from ASE Holding			0.5
Repurchase of ordinary shares			1,852,000
Repurchase of ordinary shares, price per share | $ / shares			$ 38.5
Treasury shares canceled			121,852,000
Converted bonds [member]
Disclosure of classes of share capital [line items]
Ordinary shares issued under conversion of Bonds			424,258,000
Top of range [member]
Disclosure of classes of share capital [line items]
Percentage of cash dividend on dividend distribution			30.00%

Equity - Summary of Capital Sur

Equity - Summary of Capital Surplus (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of classes of share capital [abstract]
Issuance of ordinary shares	$ 421,640	$ 12,906,401	$ 21,553,853
Merger by share exchange	3,844,942	117,693,658
Conversion of bonds payable			1,930,066
Difference between consideration and the carrying amount of the subsidiaries' net assets during actual disposal or acquisition	197,128	6,034,102	7,176,958
Capital surplus deficit distributed as cash dividends	4,463,710	136,634,161	30,660,877
Changes in percentage of ownership interest in subsidiaries	121,768	3,727,336	6,084,895
Treasury share transactions	5,957	182,354	1,151,345
Exercised employee share options	44,642	1,366,480	1,089,178
Expired share options (Notes 22 and 29)	21,103	645,978	223,454
Share of changes in capital surplus of associates	2,847	87,136	83,733
Dividends that the claim period has elapsed and unclaimed by shareholders	29	872
Capital surplus offset deficit	196,346	6,010,156	8,632,605
Employee share options	19,064	583,542	960,888
Equity component of convertible bonds			214,022
Others	1,594	48,805	155,936
Capital surplus for other purpose	20,658	632,347	1,330,846
Capital surplus	$ 4,680,714	$ 143,276,664	$ 40,624,328

Equity - Summary of Exchange Di

Equity - Summary of Exchange Differences on Translating Foreign Operations (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Balance at January 1		$ 201,310,187	$ 166,841,165	$ 165,924,980
Exchange differences on translating foreign operations	$ 7,443	227,821	(5,287,734)	(6,445,643)
Share from associates and joint venture accounted for using the equity method	4,463	136,608	264,389	(871,679)
Balance at December 31	7,155,436	219,027,922	201,310,187	166,841,165
Exchange differences on translating foreign operations [member]
Balance at January 1	(219,982)	(6,733,659)	(1,643,623)	4,492,671
Exchange differences on translating foreign operations	13,923	426,186	(4,952,815)	(5,843,856)
Share from associates and joint venture accounted for using the equity method	4,463	136,608	(137,221)	(292,438)
Disposal of associates and joint venture accounted for using the equity method	9,222	282,291
Balance at December 31	$ (192,374)	$ (5,888,574)	$ (6,733,659)	$ (1,643,623)

Equity - Summary of Unrealized

Equity - Summary of Unrealized Gain (Loss) on Available-for-sale Financial Assets (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Balance at January 1		$ 201,310,187	$ 166,841,165	$ 165,924,980
Unrealized gain (loss) arising on revaluation of available-for-sale financial assets			224,036	(248,599)
Share from associates and joint venture accounted for using the equity method	$ 4,463	136,608	264,389	(871,679)
Balance at December 31	$ 7,155,436	219,027,922	201,310,187	166,841,165
Reserve of gains and losses on remeasuring available-for-sale financial assets excluding changes in capital surplus [member]
Balance at January 1		$ 422,570	(197,314)	588,119
Unrealized gain (loss) arising on revaluation of available-for-sale financial assets			169,585	(257,240)
Cumulative loss reclassified to profit or loss on impairment of available-for-sale financial assets			50,206
Cumulative loss (gain) reclassified to profit or loss on disposal of available-for-sale financial assets			(1,517)	7,512
Share from associates and joint venture accounted for using the equity method			401,610	(535,705)
Balance at December 31			$ 422,570	$ (197,314)

Equity - Summary of Unrealize_2

Equity - Summary of Unrealized Gain (Loss) on Financial Assets at FVTOCI (Detail) - 12 months ended Dec. 31, 2018 $ in Thousands, $ in Thousands	USD ($)	TWD ($)	TWD ($)
Financial assets at fair value through other comprehensive income [line items]
Ending balance	$ 52,183	$ 1,597,323
Unrealized gain (loss) on financial assets at fair value through other comprehensive income [member]
Financial assets at fair value through other comprehensive income [line items]
Balance at January 1 per IAS 39	13,805		$ 422,570
Adjustment on initial application of IFRS 9 (Note 3)	(9,377)		$ (287,053)
Beginning balance	4,428	135,517
Debt instruments	(2,061)	(63,076)
Equity instruments	(13,019)	(398,513)
Share from associates and joint venture accounted for using the equity method	(18,140)	(555,271)
Disposal of equity instruments and transferred cumulative gain to retained earnings	(50)	(1,518)
Disposal of associates and joint venture accounted for using the equity method	(4,357)	(133,364)
Share from associates and joint venture accounted for using the equity method	36	1,118
Ending balance	$ (33,163)	$ (1,015,107)

Equity - Summary of Treasury Sh

Equity - Summary of Treasury Shares (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Beginning balance	265,883	265,883	265,883
Addition	1,852	0	0
Decrease	(194,794)	0	0
Ending balance	72,941	265,883	265,883
Shares held by subsidiaries [member]
Beginning balance	145,883	145,883	145,883
Addition		0	0
Decrease	(72,942)	0	0
Ending balance	72,941	145,883	145,883
Shares reserved for bonds conversion [member]
Beginning balance	120,000	120,000	120,000
Addition		0	0
Decrease	(120,000)	0	0
Ending balance		120,000	120,000
Equity Shares Held by Controlled Trust [member]
Addition	1,852
Decrease	(1,852)

Equity - Summary of Shares Held

Equity - Summary of Shares Held By Subsidiaries (Detail) shares in Thousands, $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)shares	Dec. 31, 2018TWD ($)shares	Dec. 31, 2017TWD ($)shares
Disclosure of subsidiaries [Line Items]
Shares Held By Subsidiaries (in thousands)	72,941	72,941	145,883
Shares Held By Subsidiaries, Value	$ 64,002	$ 1,959,107	$ 1,959,107
ASE Test Limited [member]
Disclosure of subsidiaries [Line Items]
Shares Held By Subsidiaries (in thousands)	44,100	44,100	88,200
Shares Held By Subsidiaries, Value	$ 45,107	$ 1,380,721	$ 1,380,721
J & R Holding Limited [member]
Disclosure of subsidiaries [Line Items]
Shares Held By Subsidiaries (in thousands)	23,352	23,352	46,704
Shares Held By Subsidiaries, Value	$ 12,470	$ 381,709	$ 381,709
ASE Test, Inc. [member]
Disclosure of subsidiaries [Line Items]
Shares Held By Subsidiaries (in thousands)	5,489	5,489	10,979
Shares Held By Subsidiaries, Value	$ 6,425	$ 196,677	$ 196,677
Fair value [member]
Disclosure of subsidiaries [Line Items]
Shares Held By Subsidiaries, Value	138,925	4,252,490	5,565,437
Fair value [member] | ASE Test Limited [member]
Disclosure of subsidiaries [Line Items]
Shares Held By Subsidiaries, Value	83,994	2,571,044	3,364,848
Fair value [member] | J & R Holding Limited [member]
Disclosure of subsidiaries [Line Items]
Shares Held By Subsidiaries, Value	44,476	1,361,415	1,781,749
Fair value [member] | ASE Test, Inc. [member]
Disclosure of subsidiaries [Line Items]
Shares Held By Subsidiaries, Value	$ 10,455	$ 320,031	$ 418,840

Equity - Summary of Non-control

Equity - Summary of Non-controlling Interests (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)	Dec. 31, 2018TWD ($)
Share of profit for the year	$ 39,320	$ 1,203,588	$ 1,677,941	$ 1,253,438
Balance at January 1		201,310,187	166,841,165	165,924,980
OTHER COMPREHENSIVE INCOME (LOSS)
Exchange difference on translating foreign operations	7,443	227,821	(5,287,734)	(6,445,643)
Unrealized gain on available-for-sale financial assets			224,036	(248,599)
Balance at December 31	7,155,436	219,027,922	201,310,187	166,841,165
Non-controlling interests [member]
Share of profit for the year	39,341	1,204,217	1,677,941	1,253,438
Balance at January 1		13,190,129	12,000,551	11,492,545
OTHER COMPREHENSIVE INCOME (LOSS)
Exchange difference on translating foreign operations	(6,480)	(198,365)	(334,920)	(601,787)
Unrealized gain on available-for-sale financial assets			5,763	1,129
Unrealized loss on equity instruments at FVTOCI	(782)	(23,928)
Remeasurement on defined benefit plans	(983)	(30,079)	(13,724)	8,846
Non-controlling interests arising from acquisition of subsidiaries (Note 30)	117,049	3,582,866
Acquisition of non-controlling interests in subsidiaries	(81,441)	(2,492,915)		42,857
Partial disposal of subsidiaries (Note 32)	55,311	1,693,064	(3,055)	26,436
Subsidiaries' buy back of their own outstanding ordinary shares (Note 32)	(26,197)	(801,884)		(912,886)
Non-controlling interest relating to outstanding vested employee share options granted by subsidiaries	63,268	1,936,643	263,213	927,823
Non-controlling interest relating to outstanding expired employee share options granted by subsidiaries			(159,200)
Cash dividends to non-controlling interests	(13,878)	(424,815)	(246,440)	(237,850)
Balance at December 31	576,265	17,639,487	13,190,129	12,000,551
Non-controlling interests [member] | Pre IFRS 15 [member]
Balance at January 1	430,909	13,190,129	12,000,551	11,492,545
OTHER COMPREHENSIVE INCOME (LOSS)
Balance at December 31			13,190,129	12,000,551
Non-controlling interests [member] | Adjustments arising from initial application [member]
OTHER COMPREHENSIVE INCOME (LOSS)
Adjustment on initial application of IFRS 15 (Note 3)	169				$ 5,183
Non-controlling interests [member] | Adoption of IFRS 15 [member]
Balance at January 1	$ 431,078	$ 13,195,312	12,000,551	11,492,545
OTHER COMPREHENSIVE INCOME (LOSS)
Balance at December 31			$ 13,195,312	$ 12,000,551

Profit Before Income Tax - Summ

Profit Before Income Tax - Summary of Other Operating Income and Expenses, Net (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Analysis of income and expense [abstract]
Rental income	$ 5,959	$ 182,411	$ 131,570	$ 51,607
Gains (losses) on disposal of property, plant and equipment and other assets	(479)	(14,644)	367,110	(127,159)
Impairment losses on property, plant and equipment and goodwill	(4,347)	(133,071)	(714,675)	(888,231)
Loss on damages and claims	(788)	(24,114)	(85,585)	(12,778)
Others	11,794	361,001	410,136	176,281
Other operating income and expenses, net	$ 12,139	$ 371,583	$ 108,556	$ (800,280)

Profit Before Income Tax - Su_2

Profit Before Income Tax - Summary of Other Income (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Analysis of income and expense [abstract]
Government subsidy	$ 14,242	$ 435,950	$ 341,844	$ 332,758
Interest income	15,231	466,211	306,871	230,067
Dividends income	6,220	190,397	59,039	26,411
Other income	$ 35,693	$ 1,092,558	$ 707,754	$ 589,236

Profit Before Income Tax - Su_3

Profit Before Income Tax - Summary of Other Gains, Net (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Analysis of income and expense [abstract]
Gain on remeasurement of investments accounted for using the equity method (Note 15)	$ 242,451	$ 7,421,408
Net gains on financial assets mandatorily at FVTPL	110,699	3,388,485
Gain on disposal of subsidiaries (Note 31)			$ 5,589,457
Net gains (losses) arising on financial instruments held for trading	(45,704)	(1,398,995)	(3,111,253)	$ 224,446
Net gains on financial assets designated as at FVTPL			327,351	223,113
Foreign exchange gains (losses), net	(33,180)	(1,015,615)	3,502,586	1,928,384
Impairment losses on financial assets	(17,021)	(521,010)	(50,206)	(91,886)
Others			1,518	(7,513)
Other gains and losses	$ 257,245	$ 7,874,273	$ 6,259,453	$ 2,276,544

Profit Before Income Tax - Su_4

Profit Before Income Tax - Summary of Finance Costs (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Analysis of income and expense [abstract]
Total interest expense for financial liabilities measured at amortized cost	$ 117,541	$ 3,597,932	$ 2,016,298	$ 2,510,197
Less: Amounts included in the cost of qualifying assets
Inventories related to real estate business	(381)	(11,648)	(190,137)	(238,469)
Property, plant and equipment	(1,643)	(50,309)	(51,262)	(54,191)
Investment properties	(3)	(89)	(13)
Interest expense	115,514	3,535,886	1,774,886	2,217,537
Other finance costs	1,057	32,355	24,608	43,538
Finance costs	$ 116,571	$ 3,568,241	$ 1,799,494	$ 2,261,075

Profit Before Income Tax - Su_5

Profit Before Income Tax - Summary of Capitalized Borrowing Costs (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Inventories related to real estate business [member] | Bottom of range [member]
Disclosure of detailed information about borrowings [line items]
Annual interest capitalization rates		4.35%	4.35%
Inventories related to real estate business [member] | Top of range [member]
Disclosure of detailed information about borrowings [line items]
Annual interest capitalization rates	4.35%	5.39%	6.00%
Property, plant and equipment [member] | Bottom of range [member]
Disclosure of detailed information about borrowings [line items]
Annual interest capitalization rates	1.84%	1.26%	1.15%
Property, plant and equipment [member] | Top of range [member]
Disclosure of detailed information about borrowings [line items]
Annual interest capitalization rates	4.52%	5.49%	4.42%
Investment properties [member] | Bottom of range [member]
Disclosure of detailed information about borrowings [line items]
Annual interest capitalization rates	1.84%	1.26%
Investment properties [member] | Top of range [member]
Disclosure of detailed information about borrowings [line items]
Annual interest capitalization rates	2.23%	1.97%

Profit Before Income Tax - Su_6

Profit Before Income Tax - Summary of Depreciation and Amortization (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Analysis of income and expense [Line Items]
Property, plant and equipment depreciation	$ 1,303,293	$ 39,893,786	$ 28,625,287	$ 28,961,614
Investment properties	12,828	392,667	122,231
Intangible assets amortization	78,486	2,402,450	457,666	508,823
Depreciation and amortization	1,394,607	42,688,903	29,205,184	29,470,437
Depreciation expense	1,316,121	40,286,453	28,747,518	28,961,614
Operating costs [member]
Analysis of income and expense [Line Items]
Intangible assets amortization	45,562	1,394,664	140,175	152,987
Depreciation expense	1,238,257	37,903,050	26,731,714	26,948,106
Operating expenses [member]
Analysis of income and expense [Line Items]
Intangible assets amortization	32,924	1,007,786	317,491	355,836
Depreciation expense	$ 77,864	$ 2,383,403	$ 2,015,804	$ 2,013,508

Profit Before Income Tax - Su_7

Profit Before Income Tax - Summary of Operating Expenses Directly Related to Investment Properties (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Direct operating expense from investment property [abstract]
Direct operating expenses of investment properties that generated rental income	$ 41,710	$ 1,276,751	$ 465,458

Profit Before Income Tax - Su_8

Profit Before Income Tax - Summary of Employee Benefits Expense (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Post-employment benefits
Defined contribution plans	$ 96,865	$ 2,965,054	$ 2,340,826	$ 2,356,416
Defined benefit plans	9,518	291,333	266,267	394,741
Post-employment benefits	106,383	3,256,387	2,607,093	2,751,157
Equity-settled share-based payments	7,045	215,648	438,765	470,788
Other employee benefits	2,088,874	63,940,430	51,043,198	49,525,940
Employee benefits expense	2,202,302	67,412,465	54,089,056	52,747,885
Operating costs [member]
Post-employment benefits
Employee benefits expense	1,481,972	45,363,170	35,978,403	35,588,529
Operating expense [member]
Post-employment benefits
Employee benefits expense	$ 720,330	$ 22,049,295	$ 18,110,653	$ 17,159,356

Profit Before Income Tax - Addi

Profit Before Income Tax - Additional Information (Detail) $ in Thousands, $ in Thousands	8 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)
Analysis of income and expense [Line Items]
Percentage of employees' compensation	0.20%	0.20%
Employees' compensation	$ 1,484	$ 45,430
Remuneration to directors	$ 1,113	$ 34,073
Percentage of remuneration to directors	0.15%	0.15%
Bottom of range [member]
Analysis of income and expense [Line Items]
Percentage of employees' compensation	0.01%	0.01%
Top of range [member]
Analysis of income and expense [Line Items]
Percentage of employees' compensation	1.00%	1.00%
Percentage of remuneration to directors	0.75%	0.75%

Income Tax - Summary of Major C

Income Tax - Summary of Major Components of Income Tax Expense (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Current income tax
In respect of the current year	$ 170,118	$ 5,207,309	$ 4,979,766	$ 4,177,900
Income tax on unappropriated earnings	(33,406)	(1,022,560)	1,076,353	829,345
Changes in estimate for prior years	(3,392)	(103,822)	(88,162)	28,160
Current income tax	133,320	4,080,927	5,967,957	5,035,405
Deferred income tax
In respect of the current year	(7,426)	(227,327)	534,472	574,541
Effect of tax rate changes	21,475	657,346		14,184
Changes in estimate for prior years	186	5,696	52,872	(206,788)
Effect of foreign currency exchange differences	(107)	(3,273)	(31,698)	(26,498)
Deferred income tax	14,128	432,442	555,646	355,439
Income tax expense recognized in profit or loss	$ 147,448	$ 4,513,369	$ 6,523,603	$ 5,390,844

Income Tax - Summary of Reconci

Income Tax - Summary of Reconciliation of Income Tax Expense (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Major components of tax expense (income) [abstract]
Profit before income tax	$ 1,043,374	$ 31,937,678	$ 31,020,663	$ 27,968,705
Income tax expense calculated at the statutory rates	442,359	13,540,599	10,890,498	8,634,187
Nontaxable expense (income) in determining taxable income	11,533	353,019	483,715	(34,954)
Tax-exempt income	(82,177)	(2,515,453)	(623,566)	(700,274)
Additional income tax on unappropriated earnings	(33,406)	(1,022,560)	1,076,353	829,345
Loss carry-forward and income tax credits currently used	(31,726)	(971,124)	(1,124,043)	(898,700)
Remeasurement of deferred income tax assets, net	(156,036)	(4,776,271)	(4,131,473)	(2,797,673)
Changes in estimate for prior periods	(3,392)	(103,822)	(88,162)	28,160
Withholding tax	293	8,981	40,281	81,543
Land value increment tax				249,210
Income tax expense recognized in profit or loss	$ 147,448	$ 4,513,369	$ 6,523,603	$ 5,390,844

Income Tax - Additional Informa

Income Tax - Additional Information (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016	Dec. 31, 2018TWD ($)
Disclosure of income taxes [line items]
Applied tax rate	20.00%	17.00%	17.00%
Income tax on unappropriated earnings	5.00%	10.00%
Taxable temporary differences associated with the investments in subsidiaries for which no deferred tax liabilities recognized	$ 941,224	$ 16,401,422		$ 28,810,874
Subsidiaries [member] | China [member]
Disclosure of income taxes [line items]
Applied tax rate	25.00%	25.00%
Reduction tax rate	15.00%

Income Tax - Summary of Income

Income Tax - Summary of Income Tax Recognized Directly in Equity (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Current and deferred tax relating to items charged or credited directly to equity [abstract]
Deferred income tax related to employee share options	$ (36)	$ (1,099)	$ 262	$ (204)

Income Tax - Summary of Incom_2

Income Tax - Summary of Income Tax Recognized in Other Comprehensive Income (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Income tax relating to components of other comprehensive income [abstract]
Deferred income tax Related to remeasurement of defined benefit plans	$ 1,808	$ 55,346	$ (51,217)	$ 73,637
Effect of tax rate changes	2,312	70,755
Income tax recognized in other comprehensive income	$ 4,120	$ 126,101	$ (51,217)	$ 73,637

Income Tax - Summary of Current

Income Tax - Summary of Current Tax Assets and Liabilities (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Current tax assets
Tax refund receivable	$ 1,648	$ 50,456	$ 28,458
Prepaid income tax	15,479	473,807	232,084
Current tax assets	17,127	524,263	260,542
Current tax liabilities
Income tax payable	$ 221,533	$ 6,781,136	$ 7,619,328

Income Tax - Summary of Movemen

Income Tax - Summary of Movements of Deferred Tax Assets and Deferred Tax Liabilities (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Balance at January 1	$ (31,352)	$ (959,666)	$ (319,625)	$ 168,966
Recognized in Profit or Loss	(14,128)	(432,442)	(555,646)	(355,439)
Recognized in Other Comprehensive Income	4,120	126,101	(51,217)	73,637
Recognized in Equity	(36)	(1,099)	262	(204)
Exchange Differences	3,762	115,153	(33,440)	(209,524)
Acquisitions Through Business Combinations	17,999	550,955		2,939
Balance at December 31	(22,815)	(698,356)	(959,666)	(319,625)
Property, plant and equipment [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Balance at January 1	(126,726)	(3,879,066)	(3,758,847)	(3,504,458)
Recognized in Profit or Loss	(19,609)	(600,229)	(101,576)	(182,291)
Exchange Differences	(691)	(21,146)	(18,643)	(72,098)
Acquisitions Through Business Combinations	(1,499)	(45,873)
Balance at December 31	(148,525)	(4,546,314)	(3,879,066)	(3,758,847)
Defined benefit obligation [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Balance at January 1	25,490	780,240	873,484	845,939
Recognized in Profit or Loss	(4,302)	(131,687)	(26,736)	(48,601)
Recognized in Other Comprehensive Income	4,120	126,101	(51,217)	73,637
Exchange Differences	911	27,884	(15,291)	2,509
Acquisitions Through Business Combinations	8,569	262,286
Balance at December 31	34,788	1,064,824	780,240	873,484
Mandatorily at fair value through profit or loss [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Balance at January 1	(3,427)	(104,903)	(21,363)	(232,198)
Recognized in Profit or Loss	9,300	284,659	(86,342)	212,737
Exchange Differences	(4)	(137)	2,802	(1,902)
Acquisitions Through Business Combinations	895	27,402
Balance at December 31	6,764	207,021	(104,903)	(21,363)
Other temporary differences [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Balance at January 1	33,597	1,028,409	1,079,824	1,384,987
Recognized in Profit or Loss	(854)	(26,147)	(22,748)	(283,179)
Recognized in Equity	(36)	(1,099)	262	(204)
Exchange Differences	2,428	74,327	(28,929)	(21,780)
Acquisitions Through Business Combinations	9,622	294,540
Balance at December 31	41,576	1,272,672	1,028,409	1,079,824
Temporary differences [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Balance at January 1	(71,066)	(2,175,320)	(1,826,902)	(1,505,730)
Recognized in Profit or Loss	(15,465)	(473,404)	(237,402)	(301,334)
Recognized in Other Comprehensive Income	4,120	126,101	(51,217)	73,637
Recognized in Equity	(36)	(1,099)	262	(204)
Exchange Differences	2,644	80,928	(60,061)	(93,271)
Acquisitions Through Business Combinations	17,587	538,355
Balance at December 31	(65,397)	(2,001,797)	(2,175,320)	(1,826,902)
Unused tax losses [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Balance at January 1	22,262	681,441	1,124,541	1,323,577
Recognized in Profit or Loss	(1,635)	(50,059)	(456,246)	(110,967)
Exchange Differences	924	28,293	13,146	(91,008)
Acquisitions Through Business Combinations	412	12,600		2,939
Balance at December 31	21,963	672,275	681,441	1,124,541
Unused tax credits [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Balance at January 1	17,452	534,213	382,736	351,119
Recognized in Profit or Loss	2,973	91,021	138,002	56,862
Exchange Differences	194	5,932	13,475	(25,245)
Balance at December 31	20,619	631,166	$ 534,213	$ 382,736
Adjustments arising from initial application [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Recognized in Profit or Loss	(3,181)	(97,358)
Adjustments arising from initial application [member] | Other temporary differences [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Recognized in Profit or Loss	(3,181)	(97,358)
Adjustments arising from initial application [member] | Temporary differences [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Recognized in Profit or Loss	$ (3,181)	$ (97,358)

Income Tax - Summary of Unrecog

Income Tax - Summary of Unrecognized Deferred Tax Assets Related to Loss Carry-forward, Investment Credits and Deductible Temporary Differences (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of temporary difference, unused tax losses and unused tax credits [abstract]
Loss carry-forward	$ 21,759	$ 666,043	$ 542,054
Deductible temporary differences	10,854	332,255	712,141
Unrecognized deferred tax assets	$ 32,613	$ 998,298	$ 1,254,195

Income Tax - Summary of Unused

Income Tax - Summary of Unused Loss Carry-forward (Detail) - Dec. 31, 2018 - Unused tax losses [member] $ in Thousands, $ in Thousands	USD ($)	TWD ($)
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Unused loss carry-forward	$ 43,721	$ 1,338,319
2019 [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Unused loss carry-forward	5,355	163,916
2020 [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Unused loss carry-forward	9,489	290,460
2021 [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Unused loss carry-forward	5,215	159,641
2022 [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Unused loss carry-forward	3,080	94,287
2023 and thereafter [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Unused loss carry-forward	$ 20,582	$ 630,015

Income Tax - Summary of Unuse_2

Income Tax - Summary of Unused Investment Credits (Detail) - 12 months ended Dec. 31, 2018 $ in Thousands, $ in Thousands	USD ($)	TWD ($)
Unused tax credits [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Remaining Creditable Amount	$ 20,619	$ 631,166
Purchase of machinery and equipment [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Expiry Year	2022
Purchase of machinery and equipment [member] | Unused tax credits [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Remaining Creditable Amount	$ 19,297	590,694
Others [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Expiry Year	2023 and thereafter
Others [member] | Unused tax credits [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Remaining Creditable Amount	$ 1,322	$ 40,472

Income Tax - Summary of Project

Income Tax - Summary of Projects were Exempted From Income Tax (Detail)	12 Months Ended
	Dec. 31, 2018
Construction and expansion of 2007 by the company [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Tax-exemption period, start date	2016-01
Tax-exemption period, end date	2020-12
Construction and expansion of 2007 by the company [member] | Siliconware Precision Industries Co., Ltd. [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Tax-exemption period, start date	2015-01
Tax-exemption period, end date	2019-12
Construction and expansion of 2008 [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Tax-exemption period, start date	2014-01
Tax-exemption period, end date	2018-12
Construction and expansion of 2008 [member] | ASE Test, Inc. [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Tax-exemption period, start date	2014-01
Tax-exemption period, end date	2018-12
Construction and expansion of 2008 [member] | ASE Electronics Inc. [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Tax-exemption period, start date	2016-01
Tax-exemption period, end date	2020-12
Construction and expansion of 2009 [member] | ASE Test, Inc. [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Tax-exemption period, start date	2018-01
Tax-exemption period, end date	2022-12

Earnings Per Share - Summary of

Earnings Per Share - Summary of Earnings and Weighted Average Number of Ordinary Shares Outstanding in Computation of Earnings Per Share (Detail) shares in Thousands, $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)shares	Dec. 31, 2018TWD ($)shares	Dec. 31, 2017TWD ($)shares	Dec. 31, 2016TWD ($)shares
Earnings per share [line items]
Profit for the year attributable to owners of the Company	$ 856,606	$ 26,220,721	$ 22,819,119	$ 21,324,423
Effect of potentially dilutive ordinary shares:
From subsidiaries	(13,665)	(418,295)	(813,627)	(374,359)
From the investments in associates | $			(367,687)	(494,388)
From convertible bonds | $			93,781	(1,165,506)
Earnings used in the computation of diluted earnings per share	$ 842,941	$ 25,802,426	$ 21,731,586	$ 19,290,170
Weighted average number of ordinary shares in the computation of basic earnings per share	4,245,247	4,245,247	4,080,443	3,831,435
Effect of potentially dilutive ordinary shares:
From convertible bonds			62,456	257,648
From employee share options	5,103	5,103	19,934	29,609
From employees' compensation	779	779	21,787	23,373
Weighted average number of ordinary shares in computation of diluted earnings per share	4,251,129	4,251,129	4,184,620	4,142,065
Before Retrospectively Adjusted [member]
Effect of potentially dilutive ordinary shares:
Weighted average number of ordinary shares in the computation of basic earnings per share			8,160,887	7,662,870
Effect of potentially dilutive ordinary shares:
From convertible bonds			124,911	515,295
From employee share options			39,868	59,218
From employees' compensation			43,574	46,746
Weighted average number of ordinary shares in computation of diluted earnings per share			8,369,240	8,284,129

Earnings Per Share - Additional

Earnings Per Share - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings per share [line items]
Number of shares represented by each ADS	2	2
Before Retrospectively Adjusted [member]
Earnings per share [line items]
Number of shares represented by each ADS		5	5

Share-based Payment Arrangeme_3

Share-based Payment Arrangements - Additional Information (Detail) $ / shares in Units, $ / shares in Units, $ in Thousands, $ in Thousands

1 Months Ended

4 Months Ended

8 Months Ended

12 Months Ended

Aug. 31, 2018USD ($)shares

Apr. 29, 2018$ / shares

Apr. 29, 2018$ / shares

Dec. 31, 2018USD ($)yr$ / shares

Dec. 31, 2018USD ($)yr$ / shares

Dec. 31, 2018USD ($)yrshares

Dec. 31, 2018TWD ($)shares

Dec. 31, 2017TWD ($)yr$ / shares

Dec. 31, 2016TWD ($)$ / sharesshares

Dec. 31, 2007shares

Dec. 31, 2018TWD ($)yr

Aug. 31, 2018TWD ($)

Disclosure of terms and conditions of share-based payment arrangement [Line Items]

Capital surplus decreased

$ 311

$ 9,530

Compensation cost of employee share options

$ 7,045

$ 215,648

$ 354,765

$ 470,788

ASE Mauritius Inc. option plan [member]

Disclosure of terms and conditions of share-based payment arrangement [Line Items]

Valid term of share option plans

10 years

10 years

Number of shares granted | shares

30,000,000

Reclassification from non-controlling interest to capital surplus arising from expired employee share options | $

$ 159,200

USIE option plans [member]

Disclosure of terms and conditions of share-based payment arrangement [Line Items]

Capital surplus decreased

$ 40,492

$ 40,492

$ 40,492

$ 52,388

$ 1,239,456

USISH option plans [member]

Disclosure of terms and conditions of share-based payment arrangement [Line Items]

Valid term of share option plans

10 years

10 years

Remaining contractual life of share options | yr

6.9

6.9

6.9

7.9

6.9

ASE Inc. option plans [member]

Disclosure of terms and conditions of share-based payment arrangement [Line Items]

Valid term of share option plans

10 years

10 years

Number of employee share option plans

5

5

Share option to purchase of ordinary shares | shares

0.5

0.5

Weighted average exercise price of share options | (per share)

$ 41

$ 1.3

$ 37.6

$ 36.2

Reclassification from capital surplus arising from exercised employee share options to capital surplus arising from expired employee share options | $

$ 47,087

New shares reserved for subscription by employees under cash capital increase [member]

Disclosure of terms and conditions of share-based payment arrangement [Line Items]

Options granted to employees to purchase newly issued shares, percentage

10.00%

Employee benefits expense and capital surplus arising from exercised employee share option | $

$ 84,000

Number of shares has not been exercised | shares

4,836,000

Amount reclassified from capital surplus arising from exercised employee share options to capital surplus arising from expired employee share options | $

$ 13,541

The Company Option Plans [member]

Disclosure of terms and conditions of share-based payment arrangement [Line Items]

Number of shares registered shares | shares

150,000,000

Valid term of share option plans

10 years

10 years

Percentage of cash dividend per ordinary share exceeds market price

1.50%

1.50%

Weighted average exercise price of share options | (per share)

$ 68.5

$ 2.2

Share-based Payment Arrangeme_4

Share-based Payment Arrangements - Summary of Information About ASE Inc. Option Plans (Detail)	4 Months Ended	8 Months Ended	12 Months Ended
	Apr. 29, 2018TWD ($)shares	Dec. 31, 2018TWD ($)shares	Dec. 31, 2018TWD ($)shares	Dec. 31, 2017TWD ($)shares	Dec. 31, 2016TWD ($)shares
ASE Inc. option plans [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Number of options, beginning balance | shares	135,961,000		135,961,000	210,795,000	252,607,000
Number of options, transferred to the Company in accordance with the joint share exchange agreement | shares	113,712,000
Number of options, forfeited | shares	(1,692,000)			(5,407,000)	(6,056,000)
Number of options, expired | shares				(1,790,000)
Number of options, exercised | shares	(20,557,000)			(67,637,000)	(35,756,000)
Number of options, Ending balance | shares				135,961,000	210,795,000
Number of options, exercisable, end of period | shares				85,642,000	123,007,000
Weighted average exercise price, Beginning balance	$ 30.2		$ 30.2	$ 27.3	$ 26.6
Transferred from ASE	30.9
Weighted average exercise price, Options forfeited	36.3			36.3	34.6
Weighted average exercise price, Options expired				21.1
Weighted average exercise price, Options exercised	$ 26			21	20.9
Weighted average exercise price, Ending balance				30.2	27.3
Weighted average exercise price, Options exercisable, end of period				$ 26.5	$ 20.8
The Company Option Plans [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Number of options, transferred to the Company in accordance with the joint share exchange agreement		56,856
Options granted		131,863
Number of options, forfeited		(1,582)
Number of options, exercised		(3,323)
Number of options, Ending balance		183,814	183,814
Number of options, exercisable, end of period		36,354	36,354
Transferred from ASE		$ 61.7
Options granted		56.4
Weighted average exercise price, Options forfeited		71.5
Weighted average exercise price, Options exercised		43.6
Weighted average exercise price, Ending balance		58.1	$ 58.1
Weighted average exercise price, Options exercisable, end of period		58.1	58.1
Fair value of options granted (NT$)		$ 0	$ 0
The Company Option Plans [member] | Bottom of range [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Fair value of options granted (NT$) | shares		16.28	16.28
The Company Option Plans [member] | Top of range [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Fair value of options granted (NT$) | shares		19.12	19.12

Share-based Payment Arrangeme_5

Share-based Payment Arrangements - Summary of ASE Inc. Option Plans Outstanding Share Options (Detail)	Dec. 31, 2018TWD ($)yr	Dec. 31, 2017TWD ($)yr
ASE Inc. option plans [member] | Fourth share options exercise price [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Weighted Average Remaining Contractual Life (Years) | yr	1.5	2.5
ASE Inc. option plans [member] | Fifth share options exercise price [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Range of Exercise Price Per Share	$ 73	$ 36.5
Weighted Average Remaining Contractual Life (Years) | yr	6.7	7.7
ASE Inc. option plans [member] | Bottom of range [member] | Fourth share options exercise price [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Range of Exercise Price Per Share	$ 40.8	$ 20.4
ASE Inc. option plans [member] | Top of range [member] | Fourth share options exercise price [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Range of Exercise Price Per Share	45.2	$ 22.6
The Company Option Plans [member] | First share options exercise price [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Range of Exercise Price Per Share	$ 56.4
Weighted Average Remaining Contractual Life (Years) | yr	9.9

Share-based Payment Arrangeme_6

Share-based Payment Arrangements - Summary of Information About ASE Mauritius Inc. Option Plan (Detail) - ASE Mauritius Inc. option plan [member] shares in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)shares
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Number of options, beginning balance | shares	28,470	28,470
Number of options, forfeited | shares	(250)	0
Number of options, expired | shares	(28,220)	0
Number of options, Ending balance | shares	0	28,470
Number of options, exercisable, end of year | shares	0	28,470
Weighted average exercise price, Beginning balance | $	$ 1.7	$ 1.7
Weighted average exercise price, Options forfeited | $	1.7	0
Weighted average exercise price, Options expired | $	1.7	0
Weighted average exercise price, Ending balance | $	0	1.7
Weighted average exercise price, Options exercisable, end of year | $	$ 0	$ 1.7

Share-based Payment Arrangeme_7

Share-based Payment Arrangements - Summary of Information About USIE Option Plans (Detail) - USIE option plans [member] shares in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)shares
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Number of options, beginning balance | shares	25,556	25,933	29,695
Number of options, exercised | shares	(8,845)	(377)	(3,762)
Number of options, Ending balance | shares	16,711	25,556	25,933
Number of options, exercisable, end of year | shares	16,711	25,556	25,933
Weighted average exercise price, Beginning balance | $	$ 2.2	$ 2.2	$ 2.1
Weighted average exercise price, Options exercised | $	2.2	1.9	2
Weighted average exercise price, Ending balance | $	2.1	2.2	2.2
Weighted average exercise price, Options exercisable, end of year | $	$ 2.1	$ 2.2	$ 2.2

Share-based Payment Arrangeme_8

Share-based Payment Arrangements - Summary of USIE Option Plans Outstanding Share Options (Detail) - USIE option plans [member]	Dec. 31, 2018USD ($)yr	Dec. 31, 2017USD ($)yr
First share options exercise price [member]
Disclosure of range of exercise prices of outstanding share options [Line Items]
Range of Exercise Price Per Share	$ 1.5	$ 1.5
Weighted Average Remaining Contractual Life (Years) | yr	2	3
Second and third share options exercise price [member]
Disclosure of range of exercise prices of outstanding share options [Line Items]
Weighted Average Remaining Contractual Life (Years) | yr	2.1	2.9
Second and third share options exercise price [member] | Bottom of range [member]
Disclosure of range of exercise prices of outstanding share options [Line Items]
Range of Exercise Price Per Share	$ 2.4	$ 2.4
Second and third share options exercise price [member] | Top of range [member]
Disclosure of range of exercise prices of outstanding share options [Line Items]
Range of Exercise Price Per Share	$ 2.9	$ 2.9

Share-based Payment Arrangeme_9

Share-based Payment Arrangements - Summary of Information About USISH Option Plans (Detail) - USISH option plans [member] shares in Thousands	12 Months Ended
	Dec. 31, 2018CNY (¥)shares	Dec. 31, 2017CNY (¥)shares	Dec. 31, 2016CNY (¥)shares
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Number of options, beginning balance | shares	22,341	24,997	26,627
Number of options, forfeited | shares	(804)	(2,656)	(1,630)
Number of options, Ending balance | shares	21,537	22,341	24,997
Number of options, exercisable, end of year | shares	12,884	8,896
Weighted average exercise price, Beginning balance | ¥	¥ 15.5	¥ 15.5	¥ 15.5
Weighted average exercise price, Options forfeited | ¥	15.5	15.5	15.5
Weighted average exercise price, Ending balance | ¥	15.5	15.5	¥ 15.5
Weighted average exercise price, Options exercisable, end of year | ¥	¥ 15.5	¥ 15.5

Share-based Payment Arrangem_10

Share-based Payment Arrangements - Summary of Information About New Shares Reserved for Subscription by Employees under Cash Capital Increase Option Plans (Detail) - New shares reserved for subscription by employees under cash capital increase [member] shares in Thousands	12 Months Ended
	Dec. 31, 2017TWD ($)shares
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Number of options, granted	30,000
Number of options, exercised	25,164
Fair value of options granted (NT$ per share) | $	$ 2.80

Share-based Payment Arrangem_11

Share-based Payment Arrangements - Summary of Fair Value using Black Scholes Option Pricing Model and Inputs (Detail) - New shares reserved for subscription by employees under cash capital increase [member]	12 Months Ended
	Dec. 31, 2018TWD ($)d
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Share price at the grant date	$ 36.55
Exercise price	$ 34.30
Expected volatility	27.15%
Expected lives | d	47
Expected dividend yield	0.00%
Risk free interest rate	0.37%

Share-based Payment Arrangem_12

Share-based Payment Arrangements - Summary of Fair Value using Trinomial Tree Model and Inputs (Detail) - Trinomial tree model [member]	12 Months Ended
	Dec. 31, 2018TWD ($)
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Share price at the grant date	$ 58.80
Exercise price	$ 56.40
Expected dividend yield	0.00%
Bottom of range [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Expected volatility	27.77%
Expected lives	4.8
Risk free interest rate	0.73%
Top of range [member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Expected volatility	28.86%
Expected lives	7
Risk free interest rate	0.80%

Business Combinations - Summary

Business Combinations - Summary of Subsidiary Acquired (Detail) - TLJ Intertech Inc. [member] - TWD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	May 31, 2016
Disclosure of detailed information about business combination [Line Items]
Principal Activity	Engaged in information software services
Date of Acquisition	May 3, 2016
Proportion of Voting Equity Interests Acquired	60.00%	60.00%
Cash Consideration	$ 89,998

Business Combinations - Additio

Business Combinations - Additional Information (Detail) $ / shares in Units, $ / shares in Units, $ in Thousands, $ in Thousands	1 Months Ended		12 Months Ended
	May 31, 2018$ / shares	May 31, 2018$ / shares	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2018TWD ($)	May 31, 2016TWD ($)
Disclosure of subsidiaries [Line Items]
Significant unobservable inputs discount rate			25.00%	25.00%
Revenue from continuing operations			$ 12,978,159	$ 397,261,461
Profit from continuing operations			$ 838,766	$ 25,674,641
TLJ Intertech Inc. [member]
Disclosure of subsidiaries [Line Items]
Percentage of shareholdings acquired by subsidiary			60.00%		60.00%	60.00%
Total consideration was paid to key management personnel and related parties					$ 89,998
TLJ Intertech Inc. [member] | Related parties [member]
Disclosure of subsidiaries [Line Items]
Total consideration was paid to key management personnel and related parties						$ 41,739
Siliconware Precision Industries Co., Ltd. [member]
Disclosure of subsidiaries [Line Items]
Percentage of shareholdings acquired by subsidiary	100.00%	100.00%	100.00%		100.00%
Total consideration was paid to key management personnel and related parties			$ 5,502,796		$ 168,440,585
Cash consideration | (per share)	$ 51.2	$ 1.7

Business Combinations - Summa_2

Business Combinations - Summary of Assets Acquired and Liabilities Assumed at the Date of Acquisition (Detail) - TLJ Intertech Inc. [member] $ in Thousands	Dec. 31, 2018TWD ($)
Disclosure of detailed information about business combination [Line Items]
Current assets	$ 16,645
Non-current assets	108,486
Current liabilities	(7,599)
Fair value of identifiable net assets acquired	$ 117,532

Business Combinations - Summa_3

Business Combinations - Summary of Goodwill Recognized on Acquisition (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)	Dec. 31, 2015TWD ($)
Disclosure of detailed information about business combination [Line Items]
Goodwill recognized on acquisition	$ 1,632,618	$ 49,974,446	$ 324,551	$ 9,934,494	$ 10,490,309	$ 10,506,519
TLJ Intertech Inc. [member]
Disclosure of detailed information about business combination [Line Items]
Cash Consideration		89,998
Add: Non-controlling interests		42,857
Less: Fair value of identifiable net assets acquired		(117,532)
Goodwill recognized on acquisition		$ 15,323

Business Combinations - Summa_4

Business Combinations - Summary of Net Cash Outflow on Acquisition of Subsidiaries (Detail) - TWD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of detailed information about business combination [Line Items]
Less: Cash acquired		$ (29,133)
Net cash outflow on acquisition of subsidiaries		$ (7,046,464)
TLJ Intertech Inc. [member]
Disclosure of detailed information about business combination [Line Items]
Consideration paid in cash	$ 89,998
Less: Cash acquired	(16,561)
Net cash outflow on acquisition of subsidiaries	$ 73,437

Business Combinations - Summa_5

Business Combinations - Summary of Acquisition of SPIL (Detail) - Siliconware Precision Industries Co., Ltd. [member] $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	May 31, 2018
Disclosure of detailed information about business combination [Line Items]
Principal Activity	Engaged in the assembly, testing and turnkey services of integrated circuits.
Date of Acquisition	Apr. 30, 2018
Proportion of Voting Equity Interests Acquired	100.00%	100.00%	100.00%
Consideration Transferred	$ 5,502,796	$ 168,440,585

Business Combinations - Summa_6

Business Combinations - Summary of Assets Acquired and Liabilities Assumed at the Date of Acquisition of SPIL (Detail) - Dec. 31, 2018 - Siliconware Precision Industries Co., Ltd. [member] $ in Thousands, $ in Thousands	USD ($)	TWD ($)
Disclosure of detailed information about business combination [Line Items]
Cash and cash equivalents	$ 656,288	$ 20,088,970
Trade and other receivables	517,499	15,840,649
Inventories	186,006	5,693,644
Property, plant and equipment	2,678,393	81,985,622
Intangible assets	1,024,318	31,354,386
Others	814,960	24,945,922
Trade and other payables	(645,396)	(19,755,598)
Borrowings and bonds payables	(789,192)	(24,157,174)
Others	(129,474)	(3,963,201)
Fair value of identifiable net assets acquired	$ 4,313,402	$ 132,033,220

Business Combinations - Summa_7

Business Combinations - Summary of Goodwill Recognized on Acquisition of SPIL (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)	Dec. 31, 2015TWD ($)
Disclosure of detailed information about business combination [Line Items]
Goodwill recognized on acquisition	$ 1,632,618	$ 49,974,446	$ 324,551	$ 9,934,494	$ 10,490,309	$ 10,506,519
Siliconware Precision Industries Co., Ltd. [member]
Disclosure of detailed information about business combination [Line Items]
Total consideration	5,502,796	168,440,585
Add: Non-controlling interests	117,049	3,582,866
Less: Fair value of identifiable net assets acquired	(4,313,402)	(132,033,220)
Goodwill recognized on acquisition	$ 1,306,443	$ 39,990,231

Business Combinations - Summa_8

Business Combinations - Summary of Net Cash Outflow on Acquisition of Subsidiary SPIL (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2018TWD ($)
Disclosure of detailed information about business combination [Line Items]
Less: Cash and cash equivalent acquired			$ 29,133
Net cash outflow on acquisition of subsidiaries			$ (7,046,464)
Siliconware Precision Industries Co., Ltd. [member]
Disclosure of detailed information about business combination [Line Items]
Total consideration	$ 5,502,796			$ 168,440,585
Less: Payable for consideration representing the ordinary shares originally held by ASE	(1,735,046)	$ (53,109,760)
Less: Cash and cash equivalent acquired	(656,288)	(20,088,970)
Net cash outflow on acquisition of subsidiaries	$ 3,111,462	$ 95,241,855

Business Combinations - Summa_9

Business Combinations - Summary of Impact of Acquisitions by Comprehensive Income (Detail) - 12 months ended Dec. 31, 2018 - Siliconware Precision Industries Co., Ltd. [member] $ in Thousands, $ in Thousands	USD ($)	TWD ($)
Disclosure of detailed information about business combination [Line Items]
Operating revenue	$ 2,000,906	$ 61,247,727
Profit	$ 249,179	$ 7,627,382

Disposal of Subsidiaries - Summ

Disposal of Subsidiaries - Summary of Gain on Disposal of Subsidiaries (Detail) - TWD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2017
Disclosure of gain from disposals of subsidiaries [line items]
Total consideration		$ (7,046,464)
KSDY [member]
Disclosure of gain from disposals of subsidiaries [line items]
Total consideration	$ 7,046,464
Net assets disposed of	(1,457,007)
Gain on disposal of KSDY	$ 5,589,457

Disposal of Subsidiaries - Su_2

Disposal of Subsidiaries - Summary of Analysis of Assets and Liabilities on Date Control was Lost (Detail) - KSDY [member] $ in Thousands	1 Months Ended
	Jun. 30, 2017TWD ($)
Current assets
Cash and cash equivalents	$ 29,133
Inventories related to real estate business	1,427,874
Net assets disposed of	$ 1,457,007

Equity Transaction with Non-c_2

Equity Transaction with Non-controlling Interests - Additional Information (Detail) $ / shares in Units, $ / shares in Units, shares in Thousands, $ in Thousands, $ in Thousands	Jan. 01, 2018	Aug. 31, 2018USD ($)	Jul. 31, 2018$ / shares	Jul. 31, 2018$ / shares	Mar. 31, 2018USD ($)	Jan. 31, 2018$ / sharesshares	Jan. 31, 2017TWD ($)	Feb. 29, 2016shares	Feb. 28, 2016TWD ($)$ / sharesshares	Jan. 31, 2016	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2018TWD ($)shares	Sep. 30, 2018USD ($)	Sep. 30, 2018TWD ($)	Aug. 31, 2018TWD ($)	Mar. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Oct. 13, 2017shares	Jul. 13, 2017shares	Dec. 31, 2016TWD ($)
Increase (decrease) in capital surplus		$ 311													$ 9,530
Sale of shares | shares																		323,094	101,164
Sale of shares per share | $ / shares											$ 10
Cash capital increase [member]
Sale of shares | shares											300,000	300,000
Sale of shares per share | $ / shares											$ 34.3
USI Enterprise Limited [member]
Number of shares repurchased | shares								4,501
Percentage of increase in shareholdings	96.90%					98.60%		98.80%		96.70%
Increase (decrease) in capital surplus					$ (36,839)											$ (1,127,632)				$ (1,912,887)
Number of shares approved for repurchase | shares						3,738
Shares repurchase price per share | $ / shares						$ 17.49
Universal Global Scientific Industrial Co., Ltd. [member] | USI [member]
Increase (decrease) in capital surplus | $																				$ (20,552)
Sale of shares | shares									39,603
Sale of shares per share | $ / shares									$ 20
Proceeds from issuance of shares | $									$ 792,064
Percentage of decrease in shareholdings									76.50%	99.00%
USI [member]
Percentage of increase in shareholdings							75.20%
Increase (decrease) in capital surplus | $																	$ 3,055
Cash capital increase amount | $							$ 1,000,000
Ordinary shares outstanding acquired price | (per share)			$ 18	$ 0.6
USI [member] | Cash capital increase [member]
Percentage of increase in shareholdings							75.70%
ASEN [member]
Increase (decrease) in capital surplus											$ 36,410	$ 1,114,504	$ (56,756)	$ (1,737,315)
Amount of shares transferred					$ 127,113											$ 3,871,862
Percentage of shareholdings		30.00%
Amount of shareholdings | $		$ 95,335
ASEN [member] | Bottom of range [member]
Percentage of increase in ownership					60.00%
Percentage of decrease in ownership		70.00%
ASEN [member] | Top of range [member]
Percentage of increase in ownership					100.00%
Percentage of decrease in ownership		100.00%
USI INC [member]
Increase (decrease) in capital surplus		$ (920)													$ (28,152)
Ordinary shares outstanding acquired price | (per share)			$ 35	$ 1.1

Cash Flows Information - Summar

Cash Flows Information - Summary of Non-cash Investing Activities (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Payments for property, plant and equipment
Purchase of property, plant and equipment	$ 1,277,107	$ 39,092,238	$ 23,677,682	$ 27,680,862
Increase (decrease) in prepayments for property, plant and equipment	13,141	402,255	90,560	(89,337)
Decrease (increase) in payables for property, plant and equipment	63,452	1,942,259	982,260	(823,171)
Capitalized borrowing costs	(1,643)	(50,309)	(51,262)	(54,191)
Payments for property, plant and equipment	1,352,057	41,386,443	24,699,240	26,714,163
Proceeds from disposal of property, plant and equipment
Consideration from disposal of property, plant and equipment	37,028	1,133,435	1,487,334	692,826
Decrease (increase) in other receivables	(189)	(5,791)	876	(22,626)
Proceeds from disposal of property, plant and equipment	36,839	1,127,644	1,488,210	670,200
Payments for investment properties
Purchase of investment properties	4,112	125,853	186,535
Capitalized borrowing costs	(3)	(89)	(13)
Proceeds from disposals of investment property	4,109	125,764	186,522
Payments for other intangible assets
Purchase of other intangible assets	17,565	537,659	277,825	675,144
Decrease (increase) in other payables	1,310	40,106	60,159	(120,938)
Increase in other non-current liabilities				(40,313)
Purchase of intangible assets classified as investing activities	$ 18,875	$ 577,765	337,984	$ 513,893
Net cash inflow from disposal of subsidiaries
Consideration from disposal of subsidiaries			7,046,464
Increase in other payables			3,552
Cash and cash equivalents disposed of			(29,133)
Net cash inflow from disposal of subsidiaries			$ 7,020,883

Cash Flows Information - Change

Cash Flows Information - Change in Liabilities Arising From Financing Activities (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure Of Non Cash Investing Activities [line items]
Beginning balance	$ 2,499,571	$ 76,511,879	$ 111,070,988
Financing cash flows	3,320,914	101,653,172	(19,636,346)
Non-cash changes
Acquisition through business combinations (Note 30)	789,192	24,157,174
Bonds conversion	(145,612)	(4,457,191)	(11,650,369)
Reclassification for applying IFRS 9	(42,535)	(1,301,994)
Amortization of issuance cost	7,089	216,973	325,253
Effects of foreign currency exchange	44,682	1,367,721	(3,597,647)
Ending balance	6,473,301	198,147,734	76,511,879
Short-term borrowings [member]
Disclosure Of Non Cash Investing Activities [line items]
Beginning balance	586,817	17,962,471	20,955,522
Financing cash flows	729,429	22,327,813	(2,038,993)
Non-cash changes
Acquisition through business combinations (Note 30)	118,257	3,619,858
Reclassification for applying IFRS 9	(42,535)	(1,301,994)
Effects of foreign currency exchange	21,409	655,321	(954,058)
Ending balance	1,413,377	43,263,469	17,962,471
Bonds payable [member]
Disclosure Of Non Cash Investing Activities [line items]
Beginning balance	756,053	23,142,780	36,999,903
Financing cash flows	(202,078)	(6,185,600)	(1,123,972)
Non-cash changes
Acquisition through business combinations (Note 30)	145,612	4,457,191
Bonds conversion	(145,612)	(4,457,191)	(11,650,369)
Amortization of issuance cost	940	28,756	319,463
Effects of foreign currency exchange			(1,402,245)
Ending balance	554,915	16,985,936	23,142,780
Long-term borrowings [member]
Disclosure Of Non Cash Investing Activities [line items]
Beginning balance	1,156,701	35,406,628	53,115,563
Financing cash flows	2,793,563	85,510,959	(16,473,381)
Non-cash changes
Acquisition through business combinations (Note 30)	525,323	16,080,125
Amortization of issuance cost	6,149	188,217	5,790
Effects of foreign currency exchange	23,273	712,400	(1,241,344)
Ending balance	$ 4,505,009	$ 137,898,329	$ 35,406,628

Operating Lease Arrangements -

Operating Lease Arrangements - Additional Information (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Disclosure of operating lease [line items]
Operating lease expiration	2019 to 2028	2019 to 2028
Rental expense	$ 52,052	$ 1,593,315	$ 1,193,477	$ 1,411,533
Bottom of range [member]
Disclosure of operating lease [line items]
Operating leasing periods	1 year	1 year
Top of range [member]
Disclosure of operating lease [line items]
Operating leasing periods	15 years	15 years

Operating Lease Arrangements _2

Operating Lease Arrangements - Summary of Future Minimum Lease Payments of Non-cancellable Operating Lease Agreements (Lessee) (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of finance lease and operating lease by lessee [line items]
Future minimum lease payments of non-cancellable operating lease commitments	$ 77,952	$ 2,386,102	$ 1,104,666
Less than 1 year [member]
Disclosure of finance lease and operating lease by lessee [line items]
Future minimum lease payments of non-cancellable operating lease commitments	16,661	509,994	246,026
1-5 years [member]
Disclosure of finance lease and operating lease by lessee [line items]
Future minimum lease payments of non-cancellable operating lease commitments	27,066	828,482	439,408
More than 5 years [member]
Disclosure of finance lease and operating lease by lessee [line items]
Future minimum lease payments of non-cancellable operating lease commitments	$ 34,225	$ 1,047,626	$ 419,232

Operating Lease Arrangements _3

Operating Lease Arrangements - Summary of Future Minimum Lease Payments of Non-cancellable Operating Lease Agreements (Lessor) (Detail) - Dec. 31, 2018 $ in Thousands, $ in Thousands	USD ($)	TWD ($)
Disclosure of finance lease and operating lease by lessee [line items]
Minimum lease payments	$ 145,894	$ 4,465,827
Less than 1 year [member]
Disclosure of finance lease and operating lease by lessee [line items]
Minimum lease payments	29,954	916,891
1-5 years [member]
Disclosure of finance lease and operating lease by lessee [line items]
Minimum lease payments	78,139	2,391,843
More than 5 years [member]
Disclosure of finance lease and operating lease by lessee [line items]
Minimum lease payments	$ 37,801	$ 1,157,093

Financial Instruments - Summary

Financial Instruments - Summary of Fair Value of Financial Instruments Not Measured at Fair Value but for Which Fair Value is Disclosed (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of detailed information about financial instruments [line items]
Bonds payable	$ 554,915	$ 16,985,936	$ 23,142,780
Fair value [member]
Disclosure of detailed information about financial instruments [line items]
Bonds payable	$ 559,515	$ 17,126,752	$ 23,247,085

Financial Instruments - Summa_2

Financial Instruments - Summary of Fair Value of Financial Instruments that are Measured at Fair Value on a Recurring Basis (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of detailed information about financial instruments [line items]
Financial assets designated as at FVTPL			$ 100,496
Financial assets held for trading			5,122,571
Financial assets at fair value through profit or loss	$ 258,035	$ 7,898,458	5,223,067
Available-for-sale financial assets			1,212,165
Financial assets mandatorily classified as at FVTPL	258,035	7,898,458
Financial assets at FVTOCI	52,183	1,597,323
Financial liabilities at FVTPL	1,197	36,655	677,430
Swap contracts [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets held for trading			60,538
Swap contracts [member] | Derivative financial instruments [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	50,889	1,557,714
Financial liabilities at FVTPL	949	29,058	652,107
Forward Exchange Contract [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets held for trading			61,325
Forward Exchange Contract [member] | Derivative financial instruments [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	1,048	32,070
Quoted ordinary shares [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets held for trading			4,410,732
Available-for-sale financial assets			279,791
Quoted ordinary shares [member] | Non derivative financial assets [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	168,287	5,151,255
Open-end mutual funds [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets held for trading			589,976
Available-for-sale financial assets			23,825
Open-end mutual funds [member] | Non derivative financial assets [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	19,007	581,800
Unquoted preferred shares [member] | Non derivative financial assets [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	8,984	275,000
Private-placement funds [member] | Non derivative financial assets [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	6,537	200,123
Private-placement convertible bonds [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets designated as at FVTPL			100,496
Private-placement convertible bonds [member] | Hybrid financial assets [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	3,283	100,496
Unquoted ordinary shares [member]
Disclosure of detailed information about financial instruments [line items]
Available-for-sale financial assets			662,477
Financial assets at FVTOCI, Investments in equity instruments	17,665	540,730
Limited partnership [member]
Disclosure of detailed information about financial instruments [line items]
Available-for-sale financial assets			246,072
Financial assets at FVTOCI, Investments in equity instruments	1,296	39,669
Unsecured subordinate corporate bonds [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets at FVTOCI, Investments in debt instruments	33,222	1,016,924
Forward exchange contracts [member] | Derivative financial instruments [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities at FVTPL	248	7,597	25,323
Level 1 of fair value hierarchy [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets at fair value through profit or loss			5,000,708
Available-for-sale financial assets			303,616
Financial assets mandatorily classified as at FVTPL	187,294	5,733,055
Level 1 of fair value hierarchy [member] | Quoted ordinary shares [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets held for trading			4,410,732
Available-for-sale financial assets			279,791
Level 1 of fair value hierarchy [member] | Quoted ordinary shares [member] | Non derivative financial assets [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	168,287	5,151,255
Level 1 of fair value hierarchy [member] | Open-end mutual funds [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets held for trading			589,976
Available-for-sale financial assets			23,825
Level 1 of fair value hierarchy [member] | Open-end mutual funds [member] | Non derivative financial assets [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	19,007	581,800
Level 2 of fair value hierarchy [Member]
Disclosure of detailed information about financial instruments [line items]
Financial assets at fair value through profit or loss			222,359
Financial assets mandatorily classified as at FVTPL	55,220	1,690,280
Financial liabilities at FVTPL	1,197	36,655	677,430
Level 2 of fair value hierarchy [Member] | Swap contracts [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets held for trading			60,538
Level 2 of fair value hierarchy [Member] | Swap contracts [member] | Derivative financial instruments [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	50,889	1,557,714
Financial liabilities at FVTPL	949	29,058	652,107
Level 2 of fair value hierarchy [Member] | Forward Exchange Contract [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets held for trading			61,325
Level 2 of fair value hierarchy [Member] | Forward Exchange Contract [member] | Derivative financial instruments [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	1,048	32,070
Level 2 of fair value hierarchy [Member] | Private-placement convertible bonds [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets designated as at FVTPL			100,496
Level 2 of fair value hierarchy [Member] | Private-placement convertible bonds [member] | Hybrid financial assets [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	3,283	100,496
Level 2 of fair value hierarchy [Member] | Forward exchange contracts [member] | Derivative financial instruments [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities at FVTPL	248	7,597	25,323
Level 3 of fair value hierarchy [member]
Disclosure of detailed information about financial instruments [line items]
Available-for-sale financial assets			908,549
Financial assets mandatorily classified as at FVTPL	15,521	475,123
Financial assets at FVTOCI	52,183	1,597,323
Level 3 of fair value hierarchy [member] | Unquoted preferred shares [member] | Non derivative financial assets [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	8,984	275,000
Level 3 of fair value hierarchy [member] | Private-placement funds [member] | Non derivative financial assets [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets mandatorily classified as at FVTPL	6,537	200,123
Level 3 of fair value hierarchy [member] | Unquoted ordinary shares [member]
Disclosure of detailed information about financial instruments [line items]
Available-for-sale financial assets			662,477
Financial assets at FVTOCI, Investments in equity instruments	17,665	540,730
Level 3 of fair value hierarchy [member] | Limited partnership [member]
Disclosure of detailed information about financial instruments [line items]
Available-for-sale financial assets			$ 246,072
Financial assets at FVTOCI, Investments in equity instruments	1,296	39,669
Level 3 of fair value hierarchy [member] | Unsecured subordinate corporate bonds [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets at FVTOCI, Investments in debt instruments	$ 33,222	$ 1,016,924

Financial Instruments - Additio

Financial Instruments - Additional Information (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)Customer	Dec. 31, 2018TWD ($)Customer	Dec. 31, 2017TWD ($)Customer	Dec. 31, 2016TWD ($)	Dec. 31, 2018TWD ($)
Disclosure of detailed information about financial instruments [line items]
Transfers between levels		$ 0	$ 0
Significant unobservable inputs discount rate	25.00%	25.00%
Increase percentage of significant unobservable inputs discount rate	1.00%	1.00%
Fair value of unquoted shares decreased	$ 252				$ 7,700
Fair value of bonds decreased	$ 229	$ 7,000
Number of largest customers | Customer	5	5	5
Percentage of trade receivables	36.00%		33.00%		36.00%
Bottom of range [member] | Actuarial assumption of discount rates [member]
Disclosure of detailed information about financial instruments [line items]
Significant unobservable inputs discount rate	20.00%	20.00%
Top of range [member] | Actuarial assumption of discount rates [member]
Disclosure of detailed information about financial instruments [line items]
Significant unobservable inputs discount rate	30.00%	30.00%
Floating interest rate [member]
Disclosure of detailed information about financial instruments [line items]
Increase decrease in basis points	1.00%	1.00%	1.00%	1.00%
Increase decrease in profit before tax	$ 45,671	$ 1,398,000	$ 24,000	$ 358,000
Currency risk [member]
Disclosure of detailed information about financial instruments [line items]
Value at risk	$ 4,214		101,000	69,000	$ 129,000
Exchange rate exposure	100.00%	100.00%
Other price risk [member]
Disclosure of detailed information about financial instruments [line items]
Increase decrease in profit before tax	$ 2,091	$ 64,000	$ 52,000	$ 26,000
Equity debt ratio	1.00%	1.00%	1.00%	1.00%
Increase decrease in other comprehensive income	$ 523	$ 16,000	$ 13,000	$ 13,000
Decrease in profit before income tax				510,000
Increase in profit before income tax				$ 445,000

Financial Instruments - Summa_3

Financial Instruments - Summary of Financial Assets Measured at Level 3 Fair Value (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Disclosure of fair value measurement of assets [line items]
Beginning Balance		$ 363,922,272
Ending Balance	$ 17,447,301	534,061,927	$ 363,922,272
Available-for-sale [member] | Level 3 of fair value hierarchy [member]
Disclosure of fair value measurement of assets [line items]
Beginning Balance	64,964	1,988,549
Recognized in profit or loss	(76)	(2,313)
Recognized in other comprehensive income (included in unrealized losses on financial assets at FVTOCI)	(9,384)	(287,248)
Purchases	19,027	582,436
Disposals	(6,827)	(208,978)
Ending Balance	67,704	2,072,446	1,988,549
Available-for-sale [member] | Level 3 of fair value hierarchy [member] | Equity Instruments Fair Value Other Comprehensive Income [member]
Disclosure of fair value measurement of assets [line items]
Beginning Balance	29,681	908,549	904,790	$ 741,089
Recognized in profit or loss			28	(100,734)
Recognized in other comprehensive income (included in unrealized losses on financial assets at FVTOCI)	(7,323)	(224,172)	17,284	(202,565)
Purchases	3,430	105,000	2,649	495,928
Disposals	(6,827)	(208,978)	16,202	28,928
Ending Balance	18,961	580,399	908,549	$ 904,790
Available-for-sale [member] | Level 3 of fair value hierarchy [member] | FVTPL equity instrument [member]
Disclosure of fair value measurement of assets [line items]
Recognized in profit or loss	(76)	(2,313)
Purchases	15,597	477,436
Ending Balance	15,521	475,123
Available-for-sale [member] | Level 3 of fair value hierarchy [member] | FVOCI Debt Instruments [member]
Disclosure of fair value measurement of assets [line items]
Beginning Balance	35,283	1,080,000
Recognized in other comprehensive income (included in unrealized losses on financial assets at FVTOCI)	(2,061)	(63,076)
Ending Balance	$ 33,222	$ 1,016,924	$ 1,080,000

Financial Instruments - Summa_4

Financial Instruments - Summary of Categories of Financial Instruments (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Disclosure of detailed information about financial instruments [line items]
Financial assets designated as at FVTPL			$ 100,496
Held for trading			5,122,571
Mandatorily at FVTPL	$ 258,035	$ 7,898,458
Available-for-sale financial assets			1,212,165
Held for trading	1,197	36,655	677,430
Financial liabilities for hedging	127,397	3,899,634
Measured at amortized cost (Note 2)	9,344,520	286,035,732	139,561,999
Mandatorily at fair value through profit or loss [member]
Disclosure of detailed information about financial instruments [line items]
Available-for-sale financial assets			1,212,165
Loans and receivables			$ 103,973,567
Measured at amortized cost	4,569,314	139,866,736
Financial assets at fair value through other comprehensive income, category [member]
Disclosure of detailed information about financial instruments [line items]
Equity instruments	18,961	580,399
Debt instruments	$ 33,222	$ 1,016,924

Financial Instruments - Summa_5

Financial Instruments - Summary of Interest Rate Risk (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Fair value interest rate risk [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	$ 571,237	$ 17,485,561	$ 17,552,955
Cash flow interest rate risk [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	1,076,209	32,942,747	39,880,736
Financial liabilities	$ 5,643,169	$ 172,737,393	$ 42,270,321

Financial Instruments - Summa_6

Financial Instruments - Summary of Maturity Analysis for Non-derivative Financial Liabilities (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Less than 1 month [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	$ 1,848,911	$ 56,595,145	$ 45,860,103
Less than 1 month [member] | Non interest bearing [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	1,083,177	33,156,044	30,695,797
Less than 1 month [member] | Floating interest rate [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	514,930	15,762,004	6,641,541
Less than 1 month [member] | Fixed interest rate [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	250,804	7,677,097	8,522,765
1 to 3 months [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	1,516,894	46,432,142	30,067,396
1 to 3 months [member] | Non interest bearing [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	1,126,854	34,493,000	18,387,296
1 to 3 months [member] | Floating interest rate [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	232,852	7,127,606	4,153,830
1 to 3 months [member] | Fixed interest rate [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	157,188	4,811,536	7,526,270
3 months to 1 year [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	1,066,719	32,652,272	11,177,095
3 months to 1 year [member] | Non interest bearing [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	225,387	6,899,093	4,549,468
3 months to 1 year [member] | Floating interest rate [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	833,411	25,510,718	5,101,178
3 months to 1 year [member] | Fixed interest rate [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	7,921	242,461	1,526,449
1-5 years [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	4,726,992	144,693,229	39,101,387
1-5 years [member] | Non interest bearing [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	1,874	57,375	2,807
1-5 years [member] | Floating interest rate [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	4,280,106	131,014,040	27,196,245
1-5 years [member] | Fixed interest rate [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	445,012	13,621,814	11,902,335
More than 5 years [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	149,104	4,564,069	7,538,905
More than 5 years [member] | Non interest bearing [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	6,420	196,523	176,199
More than 5 years [member] | Floating interest rate [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts			900,310
More than 5 years [member] | Fixed interest rate [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Non-derivative financial liabilities undiscounted amounts	$ 142,684	$ 4,367,546	$ 6,462,396

Financial Instruments - Summa_7

Financial Instruments - Summary of Maturity Analysis for Derivative Financial Instruments (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Less than 1 month [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled	$ 6,979	$ 213,624	$ (40,897)
Less than 1 month [member] | Forward exchange contracts [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Net settled	67	2,040	(8,820)
Gross settled	771	23,587	32,148
Less than 1 month [member] | Forward exchange contracts [member] | Inflows [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled	84,293	2,580,194	3,711,302
Less than 1 month [member] | Forward exchange contracts [member] | Outflows [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled	(83,522)	(2,556,607)	(3,679,154)
Less than 1 month [member] | Swap contracts [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled	6,208	190,037	(73,045)
Less than 1 month [member] | Swap contracts [member] | Inflows [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled	461,830	14,136,620	12,116,531
Less than 1 month [member] | Swap contracts [member] | Outflows [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled	(455,622)	(13,946,583)	(12,189,576)
1 to 3 months [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled	18,619	569,944	(164,400)
1 to 3 months [member] | Forward exchange contracts [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Net settled	53	1,620
Gross settled	188	5,764	30,458
1 to 3 months [member] | Forward exchange contracts [member] | Inflows [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled	15,240	466,489	2,169,093
1 to 3 months [member] | Forward exchange contracts [member] | Outflows [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled	(15,052)	(460,725)	(2,138,635)
1 to 3 months [member] | Swap contracts [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled	18,431	564,180	(194,858)
1 to 3 months [member] | Swap contracts [member] | Inflows [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled	301,029	9,214,500	14,434,880
1 to 3 months [member] | Swap contracts [member] | Outflows [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled	(282,598)	(8,650,320)	(14,629,738)
3 months to 1 year [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled	51,091	1,563,897	227,325
3 months to 1 year [member] | Forward exchange contracts [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled			3,499
3 months to 1 year [member] | Forward exchange contracts [member] | Inflows [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled			390,379
3 months to 1 year [member] | Forward exchange contracts [member] | Outflows [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled			(386,880)
3 months to 1 year [member] | Swap contracts [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled	51,091	1,563,897	223,826
3 months to 1 year [member] | Swap contracts [member] | Inflows [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled	1,246,662	38,160,316	36,676,224
3 months to 1 year [member] | Swap contracts [member] | Outflows [member]
Disclosure of maturity analysis for derivative financial liabilities [line items]
Gross settled	$ (1,195,571)	$ (36,596,419)	$ (36,452,398)

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) shares in Thousands, $ in Thousands, $ in Thousands	1 Months Ended			12 Months Ended
	Feb. 28, 2018USD ($)shares	Feb. 28, 2018TWD ($)shares	Feb. 29, 2016TWD ($)shares	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2016TWD ($)	Dec. 31, 2018TWD ($)
Patents and Technology License [member]
Disclosure of transactions between related parties [line items]
Amounts payable				$ 1,881			$ 93,000			$ 57,590
Deca Technologies Inc. [member] | Patents and Technology License [member]
Disclosure of transactions between related parties [line items]
Intangible assets acquired									$ 403,543
ASE Cultural and Educational Foundation [member] | Environmental charity [member]
Disclosure of transactions between related parties [line items]
Amount contributed related party transactions				$ 3,267	$ 100,000	$ 3,267	$ 100,000	$ 3,267	100,000
Associates [member]
Disclosure of transactions between related parties [line items]
Total consideration settled									875,000
Associates [member] | Employee dormitory [member]
Disclosure of transactions between related parties [line items]
Amounts payable									$ 228,500
USI Enterprise Limited [member]
Disclosure of transactions between related parties [line items]
Repurchase of outstanding ordinary shares | shares	1,283	1,283	1,801
Value of ordinary shares purchased	$ 21,341	$ 653,244	$ 1,130,650

Related Party Transactions - Su

Related Party Transactions - Summary of Compensation to Key Management Personnel (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Disclosure of transactions between related parties [abstract]
Short-term employee benefits	$ 34,015	$ 1,041,216	$ 860,631	$ 790,460
Post-employment benefits	127	3,884	2,858	4,790
Share-based payments	299	9,145		11,547
Total	$ 34,441	$ 1,054,245	$ 863,489	$ 806,797

Assets Pledged as Collateral _3

Assets Pledged as Collateral or for Security - Summary of Assets Pledged as Collateral or for Security (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)
Assets Pledged As Collateral or For Security [abstract]
Inventories related to real estate business	$ 156,685	$ 4,796,126	$ 4,822,043
Investment properties	218,230	6,680,017	7,151,382
Land use rights (long-term prepayments for lease)	212,858	6,515,576	6,813,751
Other financial assets (including current and non-current)	16,233	496,902	66,726
Total	$ 604,006	$ 18,488,621	$ 18,853,902

Significant Contingent Liabil_2

Significant Contingent Liabilities and Unrecognized Commitments - Additional Information (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2013TWD ($)	Feb. 28, 2019USD ($)	Feb. 28, 2019TWD ($)	Dec. 31, 2018TWD ($)
Disclosure of contingent liabilities [line items]
Unused letters of credit	$ 20,712		$ 20,000				$ 634,000
Committed to purchase property, plant and equipment	556,663		7,019,377				$ 17,039,458
Prepayment of property, plant and equipment	76,423	$ 2,339,308	294,194
Construction contract related to real estate business	$ 29,012	$ 888,052	$ 1,548,806
Announcing or commencing implementation of major restructuring [member]
Disclosure of contingent liabilities [line items]
Contribution to be made for environmental protection					$ 3,267	$ 100,000
Taiwan [member]
Disclosure of contingent liabilities [line items]
Contractual period for environmental protection				30 years
Contribution to be made for environmental protection				$ 3,000,000

Significant Subsequent Events -

Significant Subsequent Events - Additional Information (Detail) $ / shares in Units, $ / shares in Units, $ in Thousands, $ in Thousands	Mar. 28, 2019USD ($)$ / shares	Mar. 28, 2019TWD ($)$ / shares	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Disclosure of non-adjusting events after reporting period [line items]
Proceeds from issue of ordinary shares			$ 10,290,000
Proceeds from issue of bonds			$ 8,000,000	$ 9,000,000
Ordinary shares [member]
Disclosure of non-adjusting events after reporting period [line items]
Par value of ordinary shares | (per share)	$ 0.3	$ 10
Ordinary shares [member] | Top of range [member]
Disclosure of non-adjusting events after reporting period [line items]
Proceeds from issue of ordinary shares	$ 98,007	$ 3,000,000
Unsecured domestic bonds [member]
Disclosure of non-adjusting events after reporting period [line items]
Maturity term	Five and seven year	Five and seven year
Unsecured domestic bonds [member] | Unsecured domestic bond annual interest rates of 0.9% with maturity of 5 years [member]
Disclosure of non-adjusting events after reporting period [line items]
Proceeds from issue of bonds	$ 212,349	$ 6,500,000
Interest rate	0.90%	0.90%
Maturity term	5 years	5 years
Unsecured domestic bonds [member] | Unsecured domestic bond annual interest rates of 1.03% with maturity of 7 years [member]
Disclosure of non-adjusting events after reporting period [line items]
Proceeds from issue of bonds	$ 114,342	$ 3,500,000
Interest rate	1.03%	1.03%
Maturity term	7 years	7 years

Significant Assets and Liabil_3

Significant Assets and Liabilities Denominated in Foreign Currencies - Summary of Significant Assets and Liabilities Denominated in Foreign Currencies (Detail) ¥ in Thousands, ¥ in Thousands, $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016	Dec. 31, 2018TWD ($)	Dec. 31, 2018CNY (¥)	Dec. 31, 2018JPY (¥)	Dec. 31, 2017TWD ($)	Dec. 31, 2017CNY (¥)	Dec. 31, 2017JPY (¥)
US Dollar [member] | US dollar equals to New Taiwan dollar [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	$ 3,730,484	$ 3,065,296		$ 114,581,814			$ 91,223,195
Financial liabilities	$ 3,361,523	$ 2,902,995		103,249,185			86,393,137
Exchange Rate	US$1=NT$30.715	US$1=NT$29.76	US$1=NT$32.25
Exchange Rate	US$1=NT$30.715	US$1=NT$29.76	US$1=NT$32.25
US Dollar [member] | US dollar equals to Chinese yuan [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	$ 1,299,391	$ 1,193,369			¥ 39,910,801			¥ 35,514,653
Financial liabilities	$ 1,216,654	$ 1,007,629			¥ 37,369,521			¥ 29,987,042
Exchange Rate	US$1=CNY6.8632	US$1=CNY6.5342
Exchange Rate	US$1=CNY6.8632	US$1=CNY6.5342
Japanese Yen [Member] | Japanese yen equals to New Taiwan dollar [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets				1,227,583		¥ 4,412,591	1,322,436		¥ 5,005,435
Financial liabilities				$ 2,059,131		7,401,621	$ 1,430,822		5,415,677
Exchange Rate	JPY1=NT$0.2782	JPY1=NT$0.2642
Exchange Rate	JPY1=NT$0.2782	JPY1=NT$0.2642
Japanese Yen [Member] | Japanese yen equals to US dollar [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	$ 1,827,400	$ 2,143,530				6,568,657			8,113,284
Financial liabilities	$ 1,957,333	$ 2,271,811				¥ 7,035,704			¥ 8,598,832
Exchange Rate	JPY1=US$0.0091	JPY1=US$0.0089
Exchange Rate	JPY1=US$0.0091	JPY1=US$0.0089

Significant Assets and Liabil_4

Significant Assets and Liabilities Denominated in Foreign Currencies - Summary of Realized and Unrealized Foreign Exchange Gain (Loss) (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Disclosure of detailed information about financial instruments [line items]
Net Foreign Exchange Gain (Loss)	$ (33,868)	$ (1,036,715)	$ 3,547,811	$ 1,921,695
US Dollar [member] | US dollar equals to New Taiwan dollar [member]
Disclosure of detailed information about financial instruments [line items]
Exchange Rate	US$1=NT$30.715	US$1=NT$30.715	US$1=NT$29.76	US$1=NT$32.25
Net Foreign Exchange Gain (Loss)	$ (2,204)	$ (67,476)	$ (244,802)	$ 203,258
New Taiwan Dollar [member]
Disclosure of detailed information about financial instruments [line items]
Net Foreign Exchange Gain (Loss)	$ (27,744)	$ (849,234)	$ 4,130,243	$ 1,494,044
Chinese Yuan [member] | Chinese Yuan equals to New Taiwan dollar [member]
Disclosure of detailed information about financial instruments [line items]
Exchange Rate	CNY1=NT$4.4753	CNY1=NT$4.4753	CNY1=NT$4.5545	CNY1=NT$4.649
Net Foreign Exchange Gain (Loss)	$ (3,920)	$ (120,005)	$ (337,630)	$ 224,393

Others - Additional Information

Others - Additional Information (Detail) $ in Thousands	Dec. 20, 2013TWD ($)
Disclosure Detailed Information About Others [abstract]
Administrative fine imposed	$ 102,014

Operating Segments Informatio_2

Operating Segments Information - Summary of Segment Information (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)	Dec. 31, 2018TWD ($)
Disclosure of operating segments [line items]
Operating revenue	$ 12,123,242	$ 371,092,421	$ 290,441,208	$ 274,884,107
Interest income	15,231	466,211	306,871	230,067
Interest expense	(115,514)	(3,535,886)	(1,774,886)	(2,217,537)
Depreciation and amortization	(1,394,607)	(42,688,903)	(29,205,184)	(29,470,437)
Share of the profit or loss of associates and joint ventures	(15,689)	(480,244)	525,782	1,503,910
Impairment loss	(21,368)	(654,081)	(764,881)	(980,117)
Segment profit before income tax	1,043,374	31,937,678	31,020,663	27,968,705
Expenditures for segment assets	1,277,106	39,092,238	23,677,682	27,680,862
Investments accounted for using the equity method	304,224		48,753,751	49,824,690	$ 9,312,308
Contract assets	146,635				4,488,500
Packaging segment [member]
Disclosure of operating segments [line items]
Operating revenue	5,825,163	178,308,222	126,225,119	125,282,829
Interest income	5,448	166,761	43,744	32,499
Interest expense	(119,164)	(3,647,601)	(1,969,562)	(1,727,127)
Depreciation and amortization	(963,475)	(29,491,977)	(19,105,457)	(18,706,891)
Share of the profit or loss of associates and joint ventures	(14,925)	(456,846)	568,291	1,513,394
Impairment loss	(21,368)	(654,081)	(218,214)	(974,095)
Segment profit before income tax	583,680	17,866,431	12,065,304	13,921,640
Expenditures for segment assets	744,436	22,787,190	17,769,612	17,561,135
Investments accounted for using the equity method	298,996		48,566,333	49,597,195	9,152,290
Contract assets	113,962				3,488,372
Testing segment [member]
Disclosure of operating segments [line items]
Operating revenue	1,172,924	35,903,202	26,157,277	27,031,750
Interest income	1,801	55,108	48,532	41,405
Interest expense	(3,311)	(101,338)	(11,920)	(5,980)
Depreciation and amortization	(312,336)	(9,560,610)	(6,476,743)	(6,566,936)
Share of the profit or loss of associates and joint ventures	(764)	(23,398)	(42,509)	(9,484)
Impairment loss			(72,798)	(4,136)
Segment profit before income tax	259,800	7,952,484	6,904,067	7,226,531
Expenditures for segment assets	424,404	12,991,023	4,507,097	8,247,003
Investments accounted for using the equity method	5,228		187,418	227,495	160,018
Contract assets	32,673				$ 1,000,128
EMS segment [member]
Disclosure of operating segments [line items]
Operating revenue	4,962,116	151,890,384	133,948,016	115,395,130
Interest income	11,576	354,343	269,640	130,659
Interest expense				(44,433)
Depreciation and amortization	(67,481)	(2,065,590)	(2,133,253)	(2,759,298)
Impairment loss				(1,886)
Segment profit before income tax	203,397	6,225,984	6,883,327	4,626,263
Expenditures for segment assets	82,645	2,529,771	850,235	906,042
All other segments [member]
Disclosure of operating segments [line items]
Operating revenue	163,039	4,990,613	4,110,796	7,174,398
Interest income	11,507	352,232	214,265	37,297
Interest expense	(8,140)	(249,180)	(62,714)	(451,790)
Depreciation and amortization	(51,315)	(1,570,726)	(1,489,731)	(1,437,312)
Impairment loss			(473,869)
Segment profit before income tax	(3,503)	(107,221)	5,167,965	2,194,271
Expenditures for segment assets	25,621	784,254	550,738	966,682
Adjustments and Eliminations [member]
Disclosure of operating segments [line items]
Interest income	(15,101)	(462,233)	(269,310)	(11,793)
Interest expense	15,101	462,233	269,310	11,793
Inter-segment revenues [member] | Packaging segment [member]
Disclosure of operating segments [line items]
Operating revenue	115,369	3,531,431	4,911,026	4,929,897
Inter-segment revenues [member] | Testing segment [member]
Disclosure of operating segments [line items]
Operating revenue	6,936	212,310	184,707	243,980
Inter-segment revenues [member] | EMS segment [member]
Disclosure of operating segments [line items]
Operating revenue	1,922,132	58,836,465	47,119,404	47,721,424
Inter-segment revenues [member] | All other segments [member]
Disclosure of operating segments [line items]
Operating revenue	249,495	7,637,053	8,383,640	9,186,359
Inter-segment revenues [member] | Adjustments and Eliminations [member]
Disclosure of operating segments [line items]
Operating revenue	(2,293,932)	(70,217,259)	(60,598,777)	(62,081,660)
Operating segment [member]
Disclosure of operating segments [line items]
Operating revenue	14,417,174	441,309,680	351,039,985	336,965,767
Operating segment [member] | Packaging segment [member]
Disclosure of operating segments [line items]
Operating revenue	5,940,532	181,839,653	131,136,145	130,212,726
Operating segment [member] | Testing segment [member]
Disclosure of operating segments [line items]
Operating revenue	1,179,860	36,115,512	26,341,984	27,275,730
Operating segment [member] | EMS segment [member]
Disclosure of operating segments [line items]
Operating revenue	6,884,248	210,726,849	181,067,420	163,116,554
Operating segment [member] | All other segments [member]
Disclosure of operating segments [line items]
Operating revenue	$ 412,534	$ 12,627,666	$ 12,494,436	$ 16,360,757

Operating Segments Informatio_3

Operating Segments Information - Summary of Revenue from Major Products and Services (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Disclosure of products and services [line items]
Operating revenue	$ 12,123,242	$ 371,092,421	$ 290,441,208	$ 274,884,107
Packaging service [member]
Disclosure of products and services [line items]
Operating revenue	5,825,163	178,308,222	126,225,119	125,282,829
Testing service [member]
Disclosure of products and services [line items]
Operating revenue	1,172,924	35,903,202	26,157,277	27,031,750
Electronic components manufacturing service [member]
Disclosure of products and services [line items]
Operating revenue	4,962,116	151,890,384	133,948,016	115,395,130
Other products and services [member]
Disclosure of products and services [line items]
Operating revenue	$ 163,039	$ 4,990,613	$ 4,110,796	$ 7,174,398

Operating Segments Informatio_4

Operating Segments Information - Summary of Geographical Information (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)	Dec. 31, 2018TWD ($)
Disclosure of geographical areas [line items]
Operating revenue	$ 12,123,242	$ 371,092,421	$ 290,441,208	$ 274,884,107
Noncurrent assets, excluding financial instruments, post-employment benefit assets and deferred tax assets	10,280,594		163,752,501		$ 314,689,000
United States [Member]
Disclosure of geographical areas [line items]
Operating revenue	7,539,731	230,791,164	196,462,345	180,745,837
Taiwan [member]
Disclosure of geographical areas [line items]
Operating revenue	1,490,715	45,630,792	35,413,647	38,868,679
Noncurrent assets, excluding financial instruments, post-employment benefit assets and deferred tax assets	7,512,071		93,350,839		229,944,505
Asia [Member]
Disclosure of geographical areas [line items]
Operating revenue	1,830,484	56,031,108	30,201,332	29,896,304
Europe [Member]
Disclosure of geographical areas [line items]
Operating revenue	1,203,668	36,844,258	26,445,240	23,275,732
Other geographical areas [member]
Disclosure of geographical areas [line items]
Operating revenue	58,644	$ 1,795,099	1,918,644	$ 2,097,555
Noncurrent assets, excluding financial instruments, post-employment benefit assets and deferred tax assets	839,146		25,025,498		25,686,256
China [member]
Disclosure of geographical areas [line items]
Noncurrent assets, excluding financial instruments, post-employment benefit assets and deferred tax assets	$ 1,929,377		$ 45,376,164		$ 59,058,239

Operating Segments Informatio_5

Operating Segments Information - Additional Information (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018TWD ($)	Dec. 31, 2017TWD ($)	Dec. 31, 2016TWD ($)
Disclosure of operating segments [line items]
Operating revenue	$ 12,123,242	$ 371,092,421	$ 290,441,208	$ 274,884,107
Packaging and EMS segments [member] | Customer One [member]
Disclosure of operating segments [line items]
Operating revenue	$ 3,009,403	$ 92,117,839	$ 83,873,393	$ 66,554,659