MFS Institutional Money Market Portfolio, A Series Of The MFS Series Trust Xiv N-CSRS Certified semi-annual shareholder report (management investment company)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORMN-CSR

CERTIFIED SHAREHOLDER REPORT OF

REGISTERED MANAGEMENT INVESTMENT COMPANIES

Investment Company Act file number811-22033

MFS SERIES TRUST XIV

(Exact name of registrant as specified in charter)

111 Huntington Avenue, Boston, Massachusetts 02199

(Address of principal executive offices) (Zip code)

Christopher R. Bohane

Massachusetts Financial Services Company

111 Huntington Avenue

Boston, Massachusetts 02199

(Name and address of agents for service)

Registrant’s telephone number, including area code: (617)954-5000

Date of fiscal year end: August 31

Date of reporting period: February 28, 2019

ITEM 1. REPORTS TO STOCKHOLDERS.

Semiannual Report

February 28, 2019

MFS® Institutional Money Market Portfolio

IMM-SEM

MFS® Institutional Money Market Portfolio

CONTENTS

Letter from the Executive Chairman	1
Portfolio composition	2
Expense table	3
Portfolio of investments	4
Statement of assets and liabilities	7
Statement of operations	8
Statements of changes in net assets	9
Financial highlights	10
Notes to financial statements	11
Proxy voting policies and information	16
Quarterly portfolio disclosure	16
Further information	16
Information about fund contracts and legal claims	16
Contact information    back cover

The report is prepared for the general information of shareholders.

It is authorized for distribution to prospective investors only when preceded or accompanied by a current prospectus.

NOT FDIC INSURED• MAY LOSE VALUE• NO BANK GUARANTEE

LETTER FROM THE EXECUTIVE CHAIRMAN

Dear Shareholders:

Markets experienced a bout of volatility in late 2018 as a result of higher interest rates, international trade friction and geopolitical uncertainty surrounding issues such as

Brexit. But concern over those issues dissipated in the early months of 2019 due to a more dovish posture by the U.S. Federal Reserve, progress toward a trade pact between the United States and China, and a consensus forming in the British Parliament against ano-deal Brexit. Over the past year, U.S. equities have outperformed their global peers due in part to fiscal stimulus undertaken in late 2017 and early 2019, which helped maintain healthy levels of U.S. economic output against a backdrop of slowing global growth, though returns, on average, have been modest.

Globally, inflation remains largely subdued thanks in part to stable

oil prices, though tight labor markets are keeping investors on the lookout for its potential reappearance. Rising incomes in many developed and emerging markets are supportive of gains in consumption, though a challenging backdrop for global trade has weighed on manufacturing in most regions. Should the U.S. and China reach a comprehensive trade agreement, sentiment could improve later this year.

As a global investment manager with nearly a century of expertise, MFS® firmly believes active risk management offers downside mitigation and may help improve investment outcomes. We built our active investment platform with this belief in mind. Our long-term perspective influences nearly every aspect of our business, ensuring that our investment decisions align with the investing time horizons of our clients.

Respectfully,

Robert J. Manning

Executive Chairman

MFS Investment Management

April 16, 2019

The opinions expressed in this letter are subject to change and may not be relied upon for investment advice. No forecasts can be guaranteed.

1

PORTFOLIO COMPOSITION

Portfolio structure (u)

Composition including fixed income credit quality (a)(u)
A-1+	31.3%
A-1	68.9%
Other Assets Less Liabilities	(0.2)%

Maturity breakdown (u)
0 - 7 days	33.7%
8 - 29 days	23.6%
30 - 59 days	32.5%
60 - 89 days	10.4%
Other Assets Less Liabilities	(0.2)%

(a) Ratings are assigned to portfolio securities utilizing ratings from Moody’s, Fitch, and Standard & Poor’s rating agencies and applying the following hierarchy: If all three agencies provide a rating, the middle rating (after dropping the highest and lowest ratings) is assigned; if two of the three agencies rate a security, the lower of the two is assigned. Ratings are shown in the S&P scale. All ratings are subject to change. The fund did not hold unrated securities. The fund is not rated by these agencies.

(u) For purposes of this presentation, accrued interest, where applicable, is included.

Percentages are based on net assets as of February 28, 2019.

The portfolio is actively managed and current holdings may be different.

2

EXPENSE TABLE

Fund expenses borne by the shareholders during the period, September 1, 2018 through February 28, 2019

As a shareholder of the fund, you incur ongoing costs, including fund expenses. This example is intended to help you understand your ongoing costs (in dollars) of investing in the fund and to compare these costs with the ongoing costs of investing in other mutual funds.

The example is based on an investment of $1,000 invested at the beginning of the period and held for the entire period September 1, 2018 through February 28, 2019.

Actual Expenses

The first line of the following table provides information about actual account values and actual expenses. You may use the information in this line, together with the amount you invested, to estimate the expenses that you paid over the period. Simply divide your account value by $1,000 (for example, an $8,600 account value divided by $1,000 = 8.6), then multiply the result by the number in the first line under the heading entitled “Expenses Paid During Period” to estimate the expenses you paid on your account during this period.

Hypothetical Example for Comparison Purposes

The second line of the following table provides information about hypothetical account values and hypothetical expenses based on the fund’s actual expense ratio and an assumed rate of return of 5% per year before expenses, which is not the fund’s actual return. The hypothetical account values and expenses may not be used to estimate the actual ending account balance or expenses you paid for the period. You may use this information to compare the ongoing costs of investing in the fund and other funds. To do so, compare this 5% hypothetical example with the 5% hypothetical examples that appear in the shareholder reports of the other funds.

Please note that the expenses shown in the table are meant to highlight your ongoing costs only and do not reflect any transactional costs, such as sales charges (loads). Therefore, the second line of the table is useful in comparing ongoing costs only, and will not help you determine the relative total costs of owning different funds. In addition, if these transactional costs were included, your costs would have been higher.

	Annualized Expense Ratio		Beginning Account Value 9/01/18		Ending Account Value 2/28/19		Expenses Paid During Period (p) 9/01/18-2/28/19
Actual		0.01%		$1,000.00		$1,011.42		$0.05
Hypothetical (h)		0.01%		$1,000.00		$1,024.74		$0.05

(h) 5% fund return per year before expenses.

(p) “Expenses Paid During Period” are equal to the fund’s annualized expense ratio, as shown above, multiplied by the average account value over the period, multiplied by 181/365 (to reflect theone-half year period).

3

PORTFOLIO OF INVESTMENTS

2/28/19 (unaudited)

The Portfolio of Investments is a complete list of all securities owned by your fund. It is categorized by broad-based asset classes.

Certificates of Deposit - 3.7%
Issuer	Shares/Par		Value ($)
Major Banks - 3.7%
Toronto-Dominion Bank, 2.5%, due 4/22/2019	$	73,400,000	$	73,405,973
Toronto-Dominion Bank, 2.5%, due 4/23/2019		100,000,000		100,008,141
Total Certificates of Deposit (Identified Cost, $173,400,000)			$	173,414,114
Commercial Paper (y) - 62.9%
Automotive - 8.1%
American Honda Finance Corp., 2.541%, due 3/08/2019	$	50,000,000	$	49,973,000
American Honda Finance Corp., 2.583%, due 3/19/2019		50,000,000		49,935,716
American Honda Finance Corp., 2.557%, due 4/10/2019		23,910,000		23,842,604
American Honda Finance Corp., 2.61%, due 4/25/2019		55,000,000		54,786,539
American Honda Finance Corp., 2.612%, due 5/06/2019		19,000,000		18,911,279
Toyota Motor Credit Corp., 2.613%, due 3/15/2019		128,700,000		128,575,054
Toyota Motor Credit Corp., 2.531%, due 5/02/2019		58,300,000		58,053,814
			$	384,078,006
Business Services - 3.1%
Cisco Systems, Inc., 2.427%, due 4/11/2019 (t)	$	98,500,000	$	98,217,765
Cisco Systems, Inc., 2.46%, due 4/30/2019 (t)		50,000,000		49,789,804
			$	148,007,569
Computer Software - Systems - 4.0%
Apple, Inc., 2.511%, due 3/06/2019 (t)	$	107,800,000	$	107,757,096
Apple, Inc., 2.504%, due 3/22/2019 (t)		20,000,000		19,970,398
Apple, Inc., 2.506%, due 4/02/2019 (t)		60,300,000		60,165,018
			$	187,892,512
Conglomerates - 2.1%
Siemens Capital Co. LLC, 2.505%, due 4/01/2019 (t)	$	100,000,000	$	99,784,444
Consumer Products - 6.7%
Colgate-Palmolive Co., 2.361%, due 3/05/2019 (t)	$	105,570,000	$	105,535,381
Procter & Gamble Co., 2.45%, due 3/01/2019 (t)		100,000,000		99,993,397
Procter & Gamble Co., 2.451%, due 3/04/2019 (t)		113,430,000		113,399,954
			$	318,928,732
Energy - Integrated - 8.1%
Chevron Corp., 2.433%, due 3/19/2019 (t)	$	75,000,000	$	74,904,763
Chevron Corp., 2.424%, due 3/26/2019 (t)		50,000,000		49,913,189
Chevron Corp., 2.426%, due 4/03/2019 (t)		61,100,000		60,961,218

4

Portfolio of Investments (unaudited) – continued

Issuer	Shares/Par		Value ($)
Commercial Paper (y) - continued
Energy - Integrated - continued
Exxon Mobil Corp., 2.402%, due 3/13/2019	$	50,000,000	$	49,956,793
Exxon Mobil Corp., 2.433%, due 3/21/2019		47,950,000		47,882,590
Exxon Mobil Corp., 2.436%, due 4/03/2019		100,000,000		99,772,861
			$	383,391,414
Food & Beverages - 6.0%
Coca-Cola Co., 2.504%, due 3/21/2019 (t)	$	50,000,000	$	49,928,834
Coca-Cola Co., 2.504%, due 3/22/2019 (t)		23,000,000		22,965,676
Coca-Cola Co., 2.481%, due 5/02/2019 (t)		45,740,000		45,539,567
Coca-Cola Co., 2.535%, due 5/22/2019 (t)		67,500,000		67,106,113
Nestle Capital Corp., 2.402%, due 3/14/2019 (t)		100,000,000		99,907,211
			$	285,447,401
Major Banks - 8.9%
Bank of Montreal/Chicago Branch, 2.39%, due 3/01/2019	$	45,500,000	$	45,496,964
Commonwealth Bank of Australia, 2.6%, due 4/24/2019 (t)		50,000,000		49,808,035
Commonwealth Bank of Australia, 2.535%, due 5/21/2019 (t)		62,350,000		61,988,561
JPMorgan Securities, LLC, 2.701%, due 3/04/2019		50,000,000		49,986,561
Sumitomo Mitsui Banking Corp., 2.562%, due 3/11/2019 (t)		85,000,000		84,936,939
Sumitomo Mitsui Banking Corp., 2.496%, due 4/05/2019 (t)		83,900,000		83,692,767
Sumitomo Mitsui Banking Corp., 2.723%, due 4/11/2019 (t)		18,600,000		18,546,184
Toronto-Dominion Bank, 2.405%, due 3/01/2019 (t)		24,000,000		23,998,406
			$	418,454,417
Other Banks & Diversified Financials - 4.5%
Mizuho Bank Ltd./New York Branch, 2.732%, due 4/08/2019 (t)	$	89,000,000	$	88,762,526
Mizuho Bank Ltd./New York Branch, 2.732%, due 4/09/2019 (t)		88,200,000		87,958,234
Mizuho Bank Ltd./New York Branch, 2.699%, due 4/15/2019 (t)		35,135,000		35,023,257
			$	211,744,017
Pharmaceuticals - 7.5%
Merck & Co., Inc., 2.39%, due 3/01/2019 (t)	$	25,000,000	$	24,998,349
Merck & Co., Inc., 2.391%, due 3/04/2019 (t)		25,000,000		24,993,378
Merck & Co., Inc., 2.493%, due 3/18/2019 (t)		75,000,000		74,909,475
Merck & Co., Inc., 2.465%, due 4/01/2019 (t)		43,100,000		43,006,559
Novartis Finance Corp., 2.451%, due 3/05/2019 (t)		40,000,000		39,986,744
Novartis Finance Corp., 2.451%, due 3/06/2019 (t)		21,800,000		21,791,324
Novartis Finance Corp., 2.432%, due 3/13/2019 (t)		2,490,000		2,487,839
Novartis Finance Corp., 2.475%, due 4/01/2019 (t)		12,000,000		11,973,941
Novartis Finance Corp., 2.496%, due 4/02/2019 (t)		29,000,000		28,935,031
Novartis Finance Corp., 2.487%, due 4/08/2019 (t)		80,000,000		79,787,494
			$	352,870,134

5

Portfolio of Investments (unaudited) – continued

Issuer	Shares/Par		Value ($)
Commercial Paper (y) - continued
Retailers - 3.9%
Wal-Mart Stores, Inc., 2.391%, due 3/04/2019 (t)	$	27,869,000	$	27,861,571
Wal-Mart Stores, Inc., 2.413%, due 3/18/2019 (t)		128,900,000		128,746,996
Wal-Mart Stores, Inc., 2.424%, due 3/25/2019 (t)		27,800,000		27,753,879
			$	184,362,446
Total Commercial Paper (Identified Cost, $2,975,026,345)			$	2,974,961,092
U.S. Government Agencies and Equivalents (y) - 28.2%
Federal Farm Credit Bank, 2.432%, due 3/19/2019	$	8,200,000	$	8,190,242
Federal Home Loan Bank, 2.428%, due 3/01/2019		73,212,000		73,212,000
Federal Home Loan Bank, 2.341%, due 3/08/2019		100,000,000		99,953,722
Federal Home Loan Bank, 2.428%, due 3/13/2019		42,400,000		42,366,363
Federal Home Loan Bank, 2.399%, due 4/24/2019		15,600,000		15,543,606
U.S. Treasury Bill, 2.426%, due 3/01/2019		212,900,000		212,900,000
U.S. Treasury Bill, 2.378%, due 3/05/2019		132,400,000		132,365,426
U.S. Treasury Bill, 2.36%, due 3/07/2019		91,200,000		91,164,582
U.S. Treasury Bill, 2.307%, due 3/12/2019		150,000,000		149,892,056
U.S. Treasury Bill, 2.452%, due 4/02/2019		170,800,000		170,437,499
U.S. Treasury Bill, 2.365%, due 4/04/2019		150,000,000		149,666,706
U.S. Treasury Bill, 2.435%, due 5/16/2019		191,200,000		190,236,298
Total U.S. Government Agencies and Equivalents (Identified Cost, $1,335,933,124)			$	1,335,928,500
Repurchase Agreements - 5.2%
Goldman Sachs Repurchase Agreement, 2.55%, dated 2/28/2019, due 3/01/2019, total to be received $12,809,895 (secured by U.S. Treasury obligations valued at $13,065,182 in an individually traded account)	$	12,809,000	$	12,809,000
JPMorgan Chase & Co. Repurchase Agreement, 2.6%, dated 2/28/2019, due 3/01/2019, total to be received $87,006,197 (secured by U.S. Treasury obligations valued at $88,746,433 in an individually traded account)		87,000,000		87,000,000
Merrill Lynch Repurchase Agreement, 2.54%, dated 2/28/2019, due 3/01/2019, total to be received $147,950,295 (secured by U.S. Treasury obligations valued at $151,896,626 in an individually traded account)		147,940,000		147,940,000
Total Repurchase Agreements, at Cost and Value			$	247,749,000
Other Assets, Less Liabilities - 0.0%				37,360
Net Assets - 100.0%			$	4,732,090,066

(t) Security exempt from registration with the U.S. Securities and Exchange Commission under Section 4(2) of the Securities Act of 1933.

(y) The rate shown represents an annualized yield at time of purchase.

See Notes to Financial Statements

6

Financial Statements

STATEMENT OF ASSETS AND LIABILITIES

At 2/28/19 (unaudited)

This statement represents your fund’s balance sheet, which details the assets and liabilities comprising the total value of the fund.

Assets
Investments in unaffiliated issuers, at value (identified cost, $4,732,108,469)	$4,732,052,706
Cash	276
Receivables for
Interest	138,045
Other assets	16,888
Total assets	$4,732,207,915
Liabilities
Payable to affiliates
Investment adviser	$96
Shareholder servicing costs	222
Accrued expenses and other liabilities	117,531
Total liabilities	$117,849
Net assets	$4,732,090,066
Net assets consist of
Paid-in capital	$4,732,353,660
Total distributable earnings (loss)	(263,594	)
Net assets	$4,732,090,066
Shares of beneficial interest outstanding	4,732,282,859
Net asset value per share (net assets of $4,732,090,066 / 4,732,282,859 shares of beneficial interest outstanding)	$1.0000

See Notes to Financial Statements

7

Financial Statements

STATEMENT OF OPERATIONS

Six months ended 2/28/19 (unaudited)

This statement describes how much your fund earned in investment income and accrued in expenses. It also describes any gains and/or losses generated by fund operations.

Net investment income (loss)
Income
Interest	$58,160,619
Expenses
Shareholder servicing costs	$465
Administrative services fee	8,679
Insurance expense	16,687
Custodian fee	133,067
Shareholder communications	2,357
Audit and tax fees	16,827
Legal fees	24,349
Commitment fee	16,703
Miscellaneous	16,610
Total expenses	$235,744
Fees paid indirectly	(12,372	)
Net expenses	$223,372
Net investment income (loss)	$57,937,247
Realized and unrealized gain (loss)
Realized gain (loss) (identified cost basis)
Unaffiliated issuers	$(37,209	)
Change in unrealized appreciation or depreciation
Unaffiliated issuers	$(211,299	)
Net realized and unrealized gain (loss)	$(248,508	)
Change in net assets from operations	$57,688,739

See Notes to Financial Statements

8

Financial Statements

STATEMENTS OF CHANGES IN NET ASSETS

These statements describe the increases and/or decreases in net assets resulting from operations, any distributions, and any shareholder transactions.

Change in net assets	Six months ended 2/28/19 (unaudited)			Year ended 8/31/18
From operations
Net investment income (loss)		$57,937,247			$91,906,875
Net realized gain (loss)		(37,209	)		(156,437	)
Net unrealized gain (loss)		(211,299	)		188,144
Change in net assets from operations		$57,688,739			$91,938,582
Total distributions to shareholders (a)		$(57,937,247	)		$(91,906,875	)
Change in net assets from fund share transactions		$(816,610,873	)		$(725,248,427	)
Total change in net assets		$(816,859,381	)		$(725,216,720	)
Net assets
At beginning of period		5,548,949,447			6,274,166,167
At end of period		$4,732,090,066			$5,548,949,447

(a) Distributions from net investment income and from net realized gain are no longer required to be separately disclosed. See Note 2. For the year ended August 31, 2018, distributions from net investment income were $91,906,875.

See Notes to Financial Statements

9

Financial Statements

FINANCIAL HIGHLIGHTS

The financial highlights table is intended to help you understand the fund’s financial performance for the semiannual period and the past 5 fiscal years. Certain information reflects financial results for a single fund share. The total returns in the table represent the rate that an investor would have earned (or lost) on an investment in the fund share class (assuming reinvestment of all distributions) held for the entire period.

	Six months ended 2/28/19			Year ended
				8/31/18			8/31/17			8/31/16			8/31/15			8/31/14
	(unaudited)
Net asset value, beginning of period		$1.0000			$1.0000			$1.0000			$1.0000			$1.00			$1.00
Income (loss) from investment operations
Net investment income (loss) (d)		$0.0113			$0.0153			$0.0071			$0.0027			$0.00	(w)		$0.00	(w)
Net realized and unrealized gain (loss)		0.0001			0.0002			(0.0002	)		0.0001			0.00	(w)		0.00	(w)
Total from investment operations		$0.0114			$0.0155			$0.0069			$0.0028			$0.00	(w)		$0.00	(w)
Less distributions declared to shareholders
From net investment income		$(0.0114	)		$(0.0155	)		$(0.0069	)		$(0.0028	)		$(0.00	)(w)		$(0.00	)(w)
Contribution from adviser		$—			$—			$—			$0.0000	(w)		$—			$—
Net asset value, end of period		$1.0000			$1.0000			$1.0000			$1.0000			$1.00			$1.00
Total return (%) (r)		1.14	(n)		1.56			0.69			0.28			0.10			0.09
Ratios (%) (to average net assets) and Supplemental data:
Expenses before expense reductions (f)		0.01	(a)		0.01			0.01			0.01			0.01			0.01
Expenses after expense reductions (f)		N/A			N/A			N/A			0.01			0.01			0.01
Net investment income (loss)		2.28	(a)		1.53			0.71			0.27			0.10			0.09
Net assets at end of period (000 omitted)		$4,732,090			$5,548,949			$6,274,166			$4,622,258			$5,470,299			$5,284,981

Effective August 1, 2016, the fund no longer seeks to maintain a stable share price. The value of the fund’s shares are calculated to four decimal places and will vary reflecting the value of the fund’s investments.

(a) Annualized.

(d) Per share data is based on average shares outstanding.

(f) Ratios do not reflect reductions from fees paid indirectly, if applicable.

(n) Not annualized.

(r) Certain expenses have been reduced without which performance would have been lower.

(w) Per share amount was less than $0.0001 or, prior to 2016, $0.01.

See Notes to Financial Statements

10

NOTES TO FINANCIAL STATEMENTS

(unaudited)

(1) Business and Organization

MFS Institutional Money Market Portfolio (the fund) is a diversified series of MFS Series Trust XIV (the trust). The trust is organized as a Massachusetts business trust and is registered under the Investment Company Act of 1940, as amended, as anopen-end management investment company. This fund is available only to certain U.S. registered investment companies managed by MFS. MFS does not receive a management fee from this fund.

The fund is an investment company and accordingly follows the investment company accounting and reporting guidance of the Financial Accounting Standards Board (FASB) Accounting Standards Codification Topic 946 Financial Services – Investment Companies.

(2) Significant Accounting Policies

General– The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of increases and decreases in net assets from operations during the reporting period. Actual results could differ from those estimates. In the preparation of these financial statements, management has evaluated subsequent events occurring after the date of the fund’s Statement of Assets and Liabilities through the date that the financial statements were issued.

In August 2018, the Securities and Exchange Commission (SEC) released its Final Rule on Disclosure Update and Simplification (the “Final Rule”) which is intended to simplify an issuer’s disclosure compliance efforts by removing redundant or outdated disclosure requirements without significantly altering the mix of information provided to investors. Effective with the current reporting period, the fund adopted the Final Rule with the impacts being that the fund is no longer required to present the components of distributable earnings on the Statement of Assets and Liabilities or the sources of distributions to shareholders and the amount of undistributed net investment income on the Statements of Changes in Net Assets.

Balance Sheet Offsetting– The fund’s accounting policy with respect to balance sheet offsetting is that, absent an event of default by the counterparty or a termination of the agreement, the International Swaps and Derivatives Association (ISDA) Master Agreement, or similar agreement, does not result in an offset of reported amounts of financial assets and financial liabilities in the Statement of Assets and Liabilities across transactions between the fund and the applicable counterparty. The fund’s right to setoff may be restricted or prohibited by the bankruptcy or insolvency laws of the particular jurisdiction to which a specific master netting agreement counterparty is subject. Balance sheet offsetting disclosures, to the extent applicable to the fund, have been included in the fund’s Significant Accounting Policies note under the captions for each of the fund’sin-scope financial instruments and transactions.

Investment Valuations– Debt instruments are generally valued at an evaluated or composite bid as provided by a third-party pricing service. Short-term instruments with

11

Notes to Financial Statements (unaudited) – continued

a maturity at issuance of 60 days or less may be valued at amortized cost, which approximates market value. The Board of Trustees has delegated primary responsibility for determining or causing to be determined the value of the fund’s investments (including any fair valuation) to the adviser pursuant to valuation policies and procedures approved by the Board. If the adviser determines that reliable market quotations are not readily available, investments are valued at fair value as determined in good faith by the adviser in accordance with such procedures under the oversight of the Board. Under the fund’s valuation policies and procedures, market quotations are not considered to be readily available for most types of debt instruments. These investments are generally valued at fair value based on information from third-party pricing services.

Various inputs are used in determining the value of the fund’s assets or liabilities. These inputs are categorized into three broad levels. In certain cases, the inputs used to measure fair value may fall into different levels of the fair value hierarchy. In such cases, an investment’s level within the fair value hierarchy is based on the lowest level of input that is significant to the fair value measurement. The fund’s assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment, and considers factors specific to the investment. Level 1 includes unadjusted quoted prices in active markets for identical assets or liabilities. Level 2 includes other significant observable market-based inputs (including quoted prices for similar securities, interest rates, prepayment speed, and credit risk). Level 3 includes unobservable inputs, which may include the adviser’s own assumptions in determining the fair value of investments. The following is a summary of the levels used as of February 28, 2019 in valuing the fund’s assets or liabilities:

Financial Instruments	Level 1		Level 2		Level 3		Total
Short-Term Securities		$—		$4,732,052,706		$—		$4,732,052,706

For further information regarding security characteristics, see the Portfolio of Investments.

Repurchase Agreements– The fund enters into repurchase agreements under the terms of Master Repurchase Agreements with approved counterparties. Each repurchase agreement is recorded at cost. The fund requires that the securities collateral in a repurchase transaction be transferred to a custodian. The fund monitors, on a daily basis, the value of the collateral to ensure that its value, including accrued interest, is greater than amounts owed to the fund under each such repurchase agreement. Upon an event of default under a Master Repurchase Agreement, thenon-defaulting party may close out all transactions traded under such agreement and net amounts owed under each transaction to one net amount payable by one party to the other. Absent an event of default, the Master Repurchase Agreement does not result in an offset of reported amounts of assets and liabilities in the Statement of Assets and Liabilities across transactions between the fund and the applicable counterparty. At February 28, 2019, the fund had investments in repurchase agreements with a gross value of $247,749,000 included in investments in unaffiliated issuers in the Statement of Assets and Liabilities. The value of the related collateral exceeded the value of the repurchase agreements at period end.

12

Notes to Financial Statements (unaudited) – continued

Indemnifications– Under the fund’s organizational documents, its officers and Trustees may be indemnified against certain liabilities and expenses arising out of the performance of their duties to the fund. Additionally, in the normal course of business, the fund enters into agreements with service providers that may contain indemnification clauses. The fund’s maximum exposure under these agreements is unknown as this would involve future claims that may be made against the fund that have not yet occurred.

Investment Transactions and Income– Investment transactions are recorded on the trade date. Interest income is recorded on the accrual basis. All premium and discount is amortized or accreted for financial statement purposes in accordance with U.S. generally accepted accounting principles.

Fees Paid Indirectly– The fund’s custody fee may be reduced by a credit earned under an arrangement that measures the value of U.S. dollars deposited with the custodian by the fund. The amount of the credit, for the six months ended February 28, 2019, is shown as a reduction of total expenses in the Statement of Operations.

Tax Matters and Distributions– The fund intends to qualify as a regulated investment company, as defined under Subchapter M of the Internal Revenue Code, and to distribute all of its taxable income, including realized capital gains. As a result, no provision for federal income tax is required. The fund’s federal tax returns, when filed, will remain subject to examination by the Internal Revenue Service for a three year period. Management has analyzed the fund’s tax positions taken on federal and state tax returns for all open tax years and does not believe that there are any uncertain tax positions that require recognition of a tax liability.

Distributions to shareholders are recorded on theex-dividend date. Income and capital gain distributions are determined in accordance with income tax regulations, which may differ from U.S. generally accepted accounting principles. Certain capital accounts in the financial statements are periodically adjusted for permanent differences in order to reflect their tax character. These adjustments have no impact on net assets or net asset value per share. Temporary differences which arise from recognizing certain items of income, expense, gain or loss in different periods for financial statement and tax purposes will reverse at some time in the future. Distributions in excess of net investment income or net realized gains are temporary overdistributions for financial statement purposes resulting from differences in the recognition or classification of income or distributions for financial statement and tax purposes.

During the year ended August 31, 2018, there were no significant adjustments due to differences between book and tax accounting.

The tax character of distributions made during the current period will be determined at fiscal year end. The tax character of distributions declared to shareholders for the last fiscal year is as follows:

	Year ended 8/31/18
Ordinary income (including any short-term capital gains)		$91,906,875

13

Notes to Financial Statements (unaudited) – continued

The federal tax cost and the tax basis components of distributable earnings were as follows:

As of 2/28/19
Cost of investments	$4,732,108,469
Gross appreciation	88,248
Gross depreciation	(144,011	)
Net unrealized appreciation (depreciation)	$(55,763	)
As of 8/31/18
Capital loss carryforwards	(170,622	)
Net unrealized appreciation (depreciation)	155,536

The aggregate cost above includes prior fiscal year end tax adjustments, if applicable.

As of August 31, 2018, the fund had capital loss carryforwards available to offset future realized gains. These net capital losses may be carried forward indefinitely and their character is retained as short-term and/or long-term losses. Such losses are characterized as follows:

Short-Term $(170,622 ) 

(3) Transactions with Affiliates

Investment Adviser– The fund has an investment advisory agreement with MFS to provide overall investment management and related administrative services and facilities to the fund. MFS receives no compensation under this agreement.

Shareholder Servicing Agent– MFS Service Center, Inc. (MFSC), a wholly-owned subsidiary of MFS, provides transfer agent and recordkeeping functions in connection with the issuance, transfer, and redemption of shares of the fund under a Shareholder Servicing Agent Agreement. MFSC is not paid a fee for providing these services. MFSC receives payment from the fund forout-of-pocket expenses paid by MFSC on behalf of the fund. For the six months ended February 28, 2019, these costs amounted to $465.

Administrator– MFS provides certain financial, legal, shareholder communications, compliance, and other administrative services to the fund. Under an administrative services agreement, the fund reimburses MFS the costs incurred to provide these services. The fund pays an annual fixed amount of $17,500. The administrative services fee incurred for the six months ended February 28, 2019 was equivalent to an annual effective rate of 0.0003% of the fund’s average daily net assets.

Trustees’ and Officers’ Compensation– The fund may pay compensation to independent Trustees in the form of a retainer, attendance fees, and additional compensation to Board and Committee chairpersons. The fund does not pay compensation directly to Trustees or officers of the fund who are also officers of the investment adviser, all of whom receive remuneration for their services to the fund from MFS. Certain officers and Trustees of the fund are officers or directors of MFS, MFS Fund Distributors, Inc. (MFD), and MFSC. The independent Trustees do not currently receive compensation from the fund.

14

Notes to Financial Statements (unaudited) – continued

Other– This fund and certain other funds managed by MFS (the funds) have entered into a service agreement (the ISO Agreement) which provides for payment of fees solely by the funds to Tarantino LLC in return for the provision of services of an Independent Senior Officer (ISO) for the funds. Frank L. Tarantino serves as the ISO and is an officer of the funds and the sole member of Tarantino LLC. The funds can terminate the ISO Agreement with Tarantino LLC at any time under the terms of the ISO Agreement. For the six months ended February 28, 2019, the fee paid by the fund under this agreement was $4,457 and is included in “Miscellaneous” expense in the Statement of Operations. MFS has agreed to bear all expenses associated with office space, other administrative support, and supplies provided to the ISO.

(4) Shares of Beneficial Interest

The fund’s Declaration of Trust permits the Trustees to issue an unlimited number of full and fractional shares of beneficial interest. Transactions in fund shares were as follows:

	Six months ended 2/28/19						Year ended 8/31/18
	Shares			Amount			Shares			Amount
Shares sold		23,638,214,318			$23,636,503,185			44,054,945,582			$44,051,469,765
Shares issued to shareholders in reinvestment of distributions		57,941,152			57,937,239			91,821,254			91,815,107
Shares reacquired		(24,512,840,800	)		(24,511,051,297	)		(44,872,123,086	)		(44,868,533,299	)
Net change		(816,685,330	)		$(816,610,873	)		(725,356,250	)		$(725,248,427	)

The fund is solely invested in by other MFS funds for the purpose of investing excess cash balances on a short-term basis. The MFS funds do not invest in this fund for the purpose of exercising management or control. At the end of the period, the MFS International Value Fund, the MFS International New Discovery Fund, the MFS Growth Fund, and the MFS Emerging Market Debt Fund were the owners of record of approximately 19%, 8%, 7%, and 6%, respectively, of the value of outstanding voting shares of the fund. No other MFS fund owned more than 5% of the value of outstanding voting shares of the fund.

(5) Line of Credit

The fund and certain other funds managed by MFS participate in a $1.25 billion unsecured committed line of credit, subject to a $1 billion sublimit, provided by a syndication of banks under a credit agreement. Borrowings may be made for temporary financing needs. Interest is charged to each fund, based on its borrowings, generally at a rate equal to the higher of the Overnight Bank Funding rate or daily one month LIBOR plus an agreed upon spread. A commitment fee, based on the average daily, unused portion of the committed line of credit, is allocated among the participating funds. In addition, the fund and other funds managed by MFS have established unsecured uncommitted borrowing arrangements with certain banks for temporary financing needs. Interest is charged to each fund, based on its borrowings, at a rate equal to the Overnight Bank Funding rate plus an agreed upon spread. For the six months ended February 28, 2019, the fund’s commitment fee and interest expense were $16,703 and $0, respectively, and the commitment fees are separately reported in the Statement of Operations.

15

PROXY VOTING POLICIES AND INFORMATION

MFS votes proxies on behalf of the fund pursuant to proxy voting policies and procedures that are available without charge, upon request, by calling1-800-225-2606, by visitingmfs.com/proxyvoting, or by visiting the SEC’s Web site athttp://www.sec.gov.

Information regarding how the fund voted proxies relating to portfolio securities during the most recent twelve-month period ended June 30 is available by August 31 of each year without charge by visitingmfs.com/proxyvoting, or by visiting the SEC’s Web site athttp://www.sec.gov.

QUARTERLY PORTFOLIO DISCLOSURE

The fund files a complete schedule of portfolio holdings with the SEC for the first and third quarters of each fiscal year on Form N-Q. The fund’s Form N-Q is available on the SEC’s website athttp://www.sec.gov.

FURTHER INFORMATION

From time to time, MFS may post important information about the fund or the MFS funds on the MFS web site (mfs.com). This information is available athttps://www.mfs.com/en-us/what-we-do/announcements.html.

INFORMATION ABOUT FUND CONTRACTS AND LEGAL CLAIMS

The fund has entered into contractual arrangements with an investment adviser, administrator, distributor, shareholder servicing agent, 529 program manager (if applicable), and custodian who each provide services to the fund. Unless expressly stated otherwise, shareholders are not parties to, or intended beneficiaries of these contractual arrangements, and these contractual arrangements are not intended to create any shareholder right to enforce them against the service providers or to seek any remedy under them against the service providers, either directly or on behalf of the fund.

Under the Trust’s By-Laws and Declaration of Trust, any claims asserted against or on behalf of the MFS Funds, including claims against Trustees and Officers, must be brought in state and federal courts located within the Commonwealth of Massachusetts.

16

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If you own your MFS fund shares through a financial institution or a retirement plan, MFS® TALK, MFS® Access, or eDelivery may not be available to you.

CONTACT

WEB SITE

mfs.com

MFS TALK

1-800-637-8255

24 hours a day

ACCOUNT SERVICE AND LITERATURE

Shareholders

1-800-225-2606

Financial advisors

1-800-343-2829

Retirement plan services

1-800-637-1255

MAILING ADDRESS

MFS Service Center, Inc.

P.O. Box 219341

Kansas City, MO 64121-9341

OVERNIGHT MAIL

MFS Service Center, Inc.

Suite 219341

430 W 7th Street

Kansas City, MO 64105-1407

ITEM 2. CODE OF ETHICS.

During the period covered by this report, the Registrant has not amended any provision in its Code of Ethics (the “Code”) that relates to an element of the Code’s definitions enumerated in paragraph (b) of Item 2 of this FormN-CSR. During the period covered by this report, the Registrant did not grant a waiver, including an implicit waiver, from any provision of the Code.

ITEM 3. AUDIT COMMITTEE FINANCIAL EXPERT.

Not applicable for semi-annual reports.

ITEM 4. PRINCIPAL ACCOUNTANT FEES AND SERVICES.

Not applicable for semi-annual reports.

ITEM 5. AUDIT COMMITTEE OF LISTED REGISTRANTS.

Not applicable to the Registrant.

ITEM 6. INVESTMENTS

A schedule of investments for each series of the Registrant is included as part of the report to shareholders of such series under Item 1 of this FormN-CSR.

ITEM 7. DISCLOSURE OF PROXY VOTING POLICIES AND PROCEDURES FORCLOSED-END MANAGEMENT INVESTMENT COMPANIES.

Not applicable to the Registrant.

ITEM 8. PORTFOLIO MANAGERS OFCLOSED-END MANAGEMENT INVESTMENT COMPANIES.

Not applicable to the Registrant.

ITEM 9. PURCHASES OF EQUITY SECURITIES BYCLOSED-END MANAGEMENT INVESTMENT COMPANY AND AFFILIATED PURCHASERS.

Not applicable to the Registrant.

ITEM 10. SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS.

There were no material changes to the procedures by which shareholders may send recommendations to the Board for nominees to the Registrant’s Board since the Registrant last provided disclosure as to such procedures in response to the requirements of Item 407 (c)(2)(iv) of RegulationS-K or this Item.

ITEM 11. CONTROLS AND PROCEDURES.

(a) Based upon their evaluation of the effectiveness of the registrant’s disclosure controls and procedures (as defined in Rule30a-3(c) under the Investment Company Act of 1940 (the “Act”)) as conducted within 90 days of the filing date of this report onForm N-CSR, the registrant’s principal financial officer and principal executive officer have concluded that those disclosure controls and procedures provide reasonable assurance that the material information required to be disclosed by the registrant on this report is recorded, processed, summarized and reported within the time periods specified in the Securities and Exchange Commission’s rules and forms.

(b) There were no changes in the registrant’s internal controls over financial reporting (as defined in Rule30a-3(d) under the Act) that occurred during the second fiscal quarter of the period covered by the report that have materially affected, or are reasonably likely to materially affect, the registrant’s internal control over financial reporting.

ITEM 12. DISCLOSURE OF SECURITIES LENDING ACTIVITIES FORCLOSED-END MANAGEMENT INVESTMENT COMPANIES.

Not applicable to the Registrant.

ITEM 13. EXHIBITS.

(a) File the exhibits listed below as part of this form. Letter or number the exhibits in the sequence indicated.

(1) Any code of ethics, or amendment thereto, that is the subject of the disclosure required by Item 2, to the extent that the registrant intends to satisfy the Item 2 requirements through filing of an exhibit. Not applicable.

(2) A separate certification for each principal executive officer and principal financial officer of the registrant as required by Rule30a-2(a) under the Act (17 CFR270.30a-2): Attached hereto asEX-99.302CERT.

(3) Any written solicitation to purchase securities under Rule23c-1 under the Act (17 CFR270.23c-1) sent or given during the period covered by the report by or on behalf of the registrant to 10 or more persons. Not applicable.

(4) Change in the registrant’s independent public accountant. Not applicable.

(b) If the report is filed under Section 13(a) or 15(d) of the Exchange Act, provide the certifications required by Rule30a-2(b) under the Act (17 CFR270.30a-2(b)), Rule13a-14(b) or Rule15d-14(b) under the Exchange Act (17 CFR240.13a-14(b) or240.15d-14(b)) and Section 1350 of Chapter 63 of Title 18 of the United States Code (18 U.S.C. 1350) as an exhibit. A certification furnished pursuant to this paragraph will not be deemed “filed” for the purposes of Section 18 of the Exchange Act (15 U.S.C. 78r), or otherwise subject to the liability of that section. Such certification will not be deemed to be incorporated by reference into any filing under the Securities Act of 1933 or the Exchange Act, except to the extent that the registrant specifically incorporates it by reference: Attached hereto asEX-99.906CERT.

Notice

A copy of the Declaration of Trust, as amended, of the Registrant is on file with the Secretary of State of The Commonwealth of Massachusetts and notice is hereby given that this instrument is executed on behalf of the Registrant by an officer of the Registrant as an officer and not individually and the obligations of or arising out of this instrument are not binding upon any of the Trustees or shareholders individually, but are binding only upon the assets and property of the respective constituent series of the Registrant.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

(Registrant) MFS SERIES TRUST XIV

By (Signature and Title)*	DAVID L. DILORENZO
	David L. DiLorenzo, President

Date: April 16, 2019

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

By (Signature and Title)*	DAVID L. DILORENZO
	David L. DiLorenzo, President (Principal Executive Officer)

Date: April 16, 2019

By (Signature and Title)*	JAMES O. YOST
	James O. Yost, Treasurer (Principal Financial Officer and Accounting Officer)

Date: April 16, 2019

* Print name and title of each signing officer under his or her signature.