SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549

                                    FORM 10-Q


         (MARK ONE)

[ X ]    QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
         EXCHANGE ACT OF 1934


                For the quarterly period ended September 30, 2001

                                       or

[   ]    TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
         EXCHANGE ACT OF 1934


For the transition period from _______________ to _______________


Commission file number 0-23621



                              MKS INSTRUMENTS, INC.

             (Exact name of registrant as specified in its charter)


Massachusetts                                                04-2277512
(State or other jurisdiction                                 (I.R.S. Employer
of incorporation or organization)                            Identification No.)

Six Shattuck Road, Andover, Massachusetts                    01810
(Address of principal executive offices)                     (Zip Code)

Registrant's telephone number, including area code           (978) 975-2350

      Indicate by check mark whether the registrant: (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days.  Yes X  No   .

Number of shares outstanding of the issuer's common stock as of October 31,
2001: 37,881,027

                              MKS INSTRUMENTS, INC.
                                    FORM 10-Q
                                      INDEX


                                                                                  
PART I   FINANCIAL INFORMATION

         ITEM 1.  FINANCIAL STATEMENTS

                  Consolidated Balance Sheets -
                  September 30, 2001 and December 31, 2000

                  Consolidated Statements of Income (Loss) -
                  Three and nine months ended September 30, 2001 and 2000

                  Consolidated Statements of Cash Flows -
                  Nine months ended September 30, 2001 and 2000

                  Notes to Consolidated Financial Statements

         ITEM 2.  MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION
                  AND RESULTS OF OPERATIONS

         ITEM 3.  QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

PART II  OTHER INFORMATION

         ITEM 1.  LEGAL PROCEEDINGS

         ITEM 2.  CHANGES IN SECURITIES AND USE OF PROCEEDS

         ITEM 3.  DEFAULTS UPON SENIOR SECURITIES

         ITEM 4.  SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS

         ITEM 5.  OTHER INFORMATION

         ITEM 6.  EXHIBITS AND REPORTS ON FORM 8-K


PART I.  FINANCIAL INFORMATION

         ITEM 1.  FINANCIAL STATEMENTS

                              MKS INSTRUMENTS, INC.
                           CONSOLIDATED BALANCE SHEETS
                        (in thousands, except share data)



                                                                         September 30, 2001   December 31, 2000
                                                                         ------------------   -----------------
                                                                            (Unaudited)           (Note 1)
                                                                                        
                              ASSETS
Current assets:
    Cash and cash equivalents ....................................           $ 118,434            $ 123,082
    Short-term investments .......................................              12,678               17,904
    Trade accounts receivable, net ...............................              42,691               95,076
    Inventories ..................................................              70,548               69,165
    Deferred tax asset ...........................................               7,933                9,976
    Other current assets .........................................              13,259                4,433
                                                                             ---------            ---------
        Total current assets .....................................             265,543              319,636
    Property, plant and equipment, net ...........................              71,363               64,133
    Goodwill and acquired intangible assets, net .................              55,266               45,325
    Long-term investments ........................................              16,100               17,100
    Other assets .................................................              23,316                8,209
                                                                             ---------            ---------
        Total assets .............................................           $ 431,588            $ 454,403
                                                                             =========            =========

               LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities:
    Short-term borrowings ........................................           $  14,745            $  15,741
    Current portion of long-term debt ............................               1,392                2,783
    Current portion of capital lease obligations .................                 528                  610
    Accounts payable .............................................              10,822               23,653
    Accrued compensation .........................................               7,985               17,003
    Other accrued expenses .......................................              14,654               14,588
    Income taxes payable .........................................                  --                7,937
                                                                             ---------            ---------
        Total current liabilities ................................              50,126               82,315
Long-term debt ...................................................              11,906               11,439
Long-term portion of capital lease obligations ...................                 269                  947
Deferred tax liability ...........................................               3,745                1,663
Other liabilities ................................................               1,498                  517
Commitments and contingencies
Stockholders' equity:
    Preferred Stock, $0.01 par value, 2,000,000 shares
        authorized; none issued and outstanding ..................                  --                   --
    Common Stock, no par value, 75,000,000 shares authorized;
        37,808,673 and 36,645,665 issued and outstanding at
        September 30, 2001 and December 31, 2000, respectively ...                 113                  113
    Additional paid-in capital ...................................             280,114              263,723
    Retained earnings ............................................              83,845               93,235
    Accumulated other comprehensive income (loss) ................                 (28)                 451
                                                                             ---------            ---------
        Total stockholders' equity ...............................             364,044              357,522
                                                                             ---------            ---------
        Total liabilities and stockholders' equity ...............           $ 431,588            $ 454,403
                                                                             =========            =========






   The accompanying notes are an integral part of the consolidated financial
                                  statements.

                              MKS INSTRUMENTS, INC.
                    CONSOLIDATED STATEMENTS OF INCOME (LOSS)
                      (in thousands, except per share data)
                                   (Unaudited)



                                                                     Three Months Ended                    Nine Months Ended
                                                                        September 30                         September 30
                                                                   2001               2000              2001               2000
                                                                ---------          ---------         ---------          ---------
                                                                                    (Note 1)                             (Note 1)
                                                                                                            
Net sales .............................................         $  53,201          $ 121,769         $ 236,745          $ 326,694
Cost of sales .........................................            37,105             67,350           151,636            182,069
                                                                ---------          ---------         ---------          ---------
Gross profit ..........................................            16,096             54,419            85,109            144,625
Research and development ..............................             9,303              9,736            29,907             25,977
Selling, general and administrative ...................            17,474             18,274            54,107             50,331
Amortization of goodwill and acquired intangible assets             3,020              1,682             8,005              2,809
Goodwill impairment charge ............................                --                 --             3,720                 --
Merger expenses .......................................                --                 --             7,708                 --
Purchase of in-process research and development .......                --                310             2,340                310
                                                                ---------          ---------         ---------          ---------
Income (loss) from operations .........................           (13,701)            24,417           (20,678)            65,198
Interest expense ......................................               424                289             1,197              1,139
Interest income .......................................             1,208              1,256             4,382              3,796
Other income (expense), net ...........................            (1,246)                60            (1,246)              (257)
                                                                ---------          ---------         ---------          ---------
Income (loss) before income taxes .....................           (14,163)            25,444           (18,739)            67,598
Provision for income taxes (benefit) ..................            (5,092)             9,489            (3,381)            25,235
                                                                ---------          ---------         ---------          ---------
Net income (loss) .....................................         $  (9,071)         $  15,955         $ (15,358)         $  42,363
                                                                =========          =========         =========          =========

Historical net income (loss) per share:
    Basic .............................................         $   (0.24)         $    0.47         $   (0.41)         $    1.25
                                                                =========          =========         =========          =========
    Diluted ...........................................         $   (0.24)         $    0.44         $   (0.41)         $    1.19
                                                                =========          =========         =========          =========

Historical weighted average common shares outstanding:
    Basic .............................................            37,801             34,290            37,364             33,969
                                                                =========          =========         =========          =========
    Diluted ...........................................            37,801             35,988            37,364             35,642
                                                                =========          =========         =========          =========





   The accompanying notes are an integral part of the consolidated financial
                                  statements.

                              MKS INSTRUMENTS, INC.
                      CONSOLIDATED STATEMENTS OF CASH FLOWS
                                 (in thousands)
                                   (Unaudited)



                                                                                     Nine Months Ended
                                                                                       September 30,
                                                                                  2001               2000
                                                                               ---------          ---------
                                                                                                   (Note 1)
                                                                                            
Cash flows from operating activities:
    Net income (loss) ................................................         $ (15,358)         $  42,363
    Adjustments to reconcile net income (loss) to net cash provided by
      operating activities:
        Depreciation and amortization ................................            16,681             10,210
        Goodwill impairment charge ...................................             3,720                 --
        Purchase of in-process research and development ..............             2,340                310
        Loss (gain) on disposal of assets ............................             1,246                471
        Other ........................................................                21               (392)
        Changes in operating assets and liabilities net of effects of
         businesses acquired:
           Trade accounts receivable .................................            52,921            (32,637)
           Inventories ...............................................             3,261            (19,362)
           Other current assets ......................................            (9,359)            (1,523)
           Accrued expenses and other current liabilities ............           (18,673)            12,719
           Accounts payable ..........................................           (13,644)             7,591
                                                                               ---------          ---------
    Net cash provided by operating activities ........................            23,156             19,750
                                                                               ---------          ---------
    Cash flows from investing activities:
        Purchases of investments, net ................................            (3,063)            (3,419)
        Purchases of property, plant and equipment ...................           (12,564)           (20,795)
        Increase in other assets .....................................            (3,754)              (735)
        Proceeds from disposal of assets .............................             4,514                 15
        Purchases of companies, net of cash acquired .................            (7,842)           (23,784)
                                                                               ---------          ---------
    Net cash used in investing activities ............................           (22,709)           (48,718)
                                                                               ---------          ---------
    Cash flows from financing activities:
        Proceeds from short-term borrowings ..........................            23,262             17,151
        Payments on short-term borrowings ............................           (27,346)            (1,611)
        Proceeds from long-term debt .................................               833                 --
        Principal payments on long-term debt .........................            (2,073)            (4,777)
        Proceeds from exercise of stock options ......................             3,595              5,309
        Cash distributions to stockholders ...........................                --             (1,417)
        Principal payments under capital lease obligations ...........              (599)              (839)
                                                                               ---------          ---------
    Net cash provided by (used in) financing activities ..............            (2,328)            13,816
                                                                               ---------          ---------
    Effect of exchange rate changes on cash and cash equivalents .....               375               (579)
                                                                               ---------          ---------
    Decrease in cash and cash equivalents ............................            (1,506)           (15,731)
    Cash and cash equivalents at beginning of period .................           123,082             67,489
    Effect of excluded results of ASTeX (Note 1) .....................            (3,142)                --
                                                                               ---------          ---------
    Cash and cash equivalents at end of period .......................         $ 118,434          $  51,758
                                                                               =========          =========
    Supplemental disclosure of cash flow information:
        Cash paid during the period for:
           Interest ..................................................         $     855          $   1,044
                                                                               =========          =========
           Income taxes ..............................................         $  13,004          $  17,076
                                                                               =========          =========
        Noncash transactions during the period:
           Stock and options issued for acquisitions .................         $  12,110          $   8,433
                                                                               =========          =========
           Note receivable from disposal of assets ...................         $   3,900          $      --
                                                                               =========          =========





   The accompanying notes are an integral part of the consolidated financial
                                  statements.

                              MKS INSTRUMENTS, INC.
                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS
                  (Tables in thousands, except per share data)

1)       Basis of Presentation

         The interim financial data as of September 30, 2001 and for the three
         and nine months ended September 30, 2001 and 2000 is unaudited;
         however, in the opinion of MKS Instruments, Inc., the interim data
         includes all adjustments, consisting only of normal recurring
         adjustments, necessary for a fair presentation of the results for the
         interim periods. The terms "MKS" and the "Company" refer to MKS
         Instruments, Inc. and subsidiaries, including Applied Science and
         Technology, Inc. ("ASTeX"). The unaudited financial statements
         presented herein have been prepared in accordance with the instructions
         to Form 10-Q and do not include all the information and note
         disclosures required by generally accepted accounting principles. The
         financial statements should be read in conjunction with the December
         31, 2000 audited financial statements and notes thereto included in the
         MKS Annual Report on Form 10-K filed with the Securities and Exchange
         Commission on April 2, 2001 and the MKS Current Reports on Form 8-K
         filed with the Securities and Exchange Commission on April 20, 2001.

         On January 26, 2001, MKS completed its acquisition of ASTeX in a
         transaction accounted for under the pooling of interests method of
         accounting. Under the terms of the agreement, each outstanding share of
         ASTeX common stock was exchanged for 0.7669 newly issued shares of
         common stock of MKS Instruments, Inc., resulting in the issuance of
         approximately 11.2 million shares of common stock of MKS Instruments,
         Inc., representing approximately 30% of its then outstanding shares.
         There were no material adjustments required to conform the accounting
         policies of the two companies. The unaudited financial statements for
         the three months and nine months ended September 30, 2000 combine the
         historical financial statements of MKS Instruments, Inc. for the three
         months and nine months ended September 30, 2000 with the historical
         financial statements of ASTeX for the three months and nine months
         ended March 25, 2000. The following table presents details of the
         results of operations for the separate companies.



                                   MKS Instruments, Inc.            ASTeX
                                    Three months ended        Three months ended
                                    September 30, 2000          March 25, 2000               Combined
                                    ------------------          --------------               --------
                                                                                    
         Net sales ...........           $ 87,636                  $ 34,133                  $121,769
         Net income ..........           $ 12,436                  $  3,519                  $ 15,955





                                   MKS Instruments, Inc.            ASTeX
                                     Nine months ended        Nine months ended
                                    September 30, 2000          March 25, 2000               Combined
                                    ------------------          --------------               --------
                                                                                    
         Net sales ...........           $230,893                  $ 95,801                  $326,694
         Net income ..........           $ 33,053                  $  9,310                  $ 42,363


         The December 31, 2000 Balance Sheet combines the balance sheet of MKS
         Instruments, Inc. as of December 31, 2000 with the balance sheet of
         ASTeX as of July 1, 2000.

         As a result of conforming dissimilar fiscal year-ends, the ASTeX
         results of operations for the six-month period ended December 31, 2000
         are excluded from the consolidated financial statements of MKS for the
         year ended December 31, 2000. The following is information related to
         the ASTeX financial results for the six-month period ended December 31,
         2000:


                                                                                         
         Net sales................................................................................ $89,193
         Net income...............................................................................   5,968
         Net cash used by operating activities....................................................  (3,500)
         Net cash provided by investing activities................................................     245
         Net cash provided by financing activities................................................      43


                              MKS INSTRUMENTS, INC.
            NOTES TO CONSOLIDATED FINANCIAL STATEMENTS - (Continued)
                  (Tables in thousands, except per share data)


         Included in stockholders' equity at September 30, 2001 is a $5,968,000
         adjustment resulting from conforming the two companies' dissimilar year
         ends, which represents the ASTeX results of operations for the
         six-month period ended December 31, 2000.

2)       Use of Estimates

         The preparation of financial statements in conformity with 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
         dates of the financial statements and the reported amounts of revenues
         and expenses during the reporting periods. Actual results could differ
         from those estimates.

3)       Recent Accounting Pronouncements

         In July 2001, the Financial Accounting Standards Board ("FASB") issued
         Statement of Financial Accounting Standards No. 141 ("SFAS 141"),
         "Business Combinations." SFAS 141 requires the purchase method of
         accounting for business combinations initiated after June 30, 2001 and
         eliminates the pooling of interests method.

         In July 2001, the FASB issued Statement of Financial Accounting
         Standards No. 142 ("SFAS 142"), "Goodwill and Other Intangible Assets",
         which is effective for MKS on January 1, 2002. SFAS 142 requires, among
         other things, the discontinuance of goodwill amortization and includes
         provisions for the reclassification of certain existing recognized
         intangibles as goodwill, reassessment of the useful lives of existing
         recognized intangibles, and reclassification of certain intangibles out
         of previously reported goodwill. SFAS 142 also requires the Company to
         complete a transitional goodwill impairment test six months from the
         date of adoption. As a result of implementing SFAS 142, the Company
         expects to stop amortizing goodwill effective January 1, 2002 but will
         continue to amortize other intangible assets. The Company is currently
         reviewing the potential additional impact of SFAS 142 on its financial
         position and results of operations.

         In August 2001, the FASB issued SFAS No. 143 ("SFAS 143"), "Accounting
         for Asset Retirement Obligations." SFAS 143 addresses financial
         accounting and reporting for obligations associated with the retirement
         of tangible long-lived assets and the associated asset retirement
         costs. SFAS 143 is effective for financial statements issued for fiscal
         years beginning after June 15, 2002. Management is currently
         determining what effect, if any, SFAS 143 will have on its financial
         position and results of operations.

         In October 2001, the FASB issued SFAS No. 144, ("SFAS 144"),
         "Accounting for the Impairment or Disposal of Long-Lived Assets." SFAS
         144 supersedes FASB Statement No. 121, "Accounting for the Impairment
         of Long-Lived Assets and for Long Lived Assets to Be Disposed of."
         SFAS 144 applies to all long-lived assets (including discontinued
         operations) and consequently amends Accounting Principles Board Opinion
         No. 30, "Reporting Results of Operations - Reporting the Effects of
         Disposal of a Segment of a Business." SFAS 144 is effective for
         financial statements issued for fiscal years beginning after December
         15, 2001, and will thus be adopted by the Company, as required, on
         January 1, 2002. Management is currently determining what effect, if
         any, SFAS 144 will have on its financial position and results of
         operations.

4)       Cash and Cash Equivalents and Investments

         Cash equivalents consist of the following:



                                                                      September 30,      December 31,
                                                                          2001               2000
                                                                          ----               ----
                                                                                   
         Cash and Money Market Instruments ..................           $ 86,003           $ 36,687
         Commercial Paper ...................................             14,931             74,895
         Federal Government and Government Agency Obligations              3,000              1,000
         State and Municipal Government Obligations .........              8,500              2,000
         Corporate Obligations ..............................              6,000              8,500
                                                                        --------           --------
                                                                        $118,434           $123,082
                                                                        ========           ========


         Short-term available-for-sale investments maturing within one year
         consist of the following:



                                                                     September 30,      December 31,
                                                                          2001              2000
                                                                          ----              ----
                                                                                  
         Federal Government and Government Agency Obligations           $ 2,000           $10,101
         State and Municipal Government Obligations .........            10,665                --
         Corporate Obligations ..............................                --             1,000
         Commercial Paper ...................................                13             6,803
                                                                        -------           -------
                                                                        $12,678           $17,904
                                                                        =======           =======



         Long-term available-for-sale investments maturing within two years
         consist of the following:



                                                                     September 30,      December 31,
                                                                          2001              2000
                                                                          ----              ----
                                                                                  
         Federal Government and Government Agency Obligations           $ 2,000           $ 4,000
         State and Municipal Government Obligations .........            14,100            13,100
                                                                        -------           -------
                                                                        $16,100           $17,100
                                                                        =======           =======


5)       Net Income (Loss) Per Share

         The following is a reconciliation of basic to diluted net income (loss)
         per share:



                                                                      Three Months Ended September 30,
                                                                          2001                2000
                                                                          ----                ----
                                                                                      
         Net income (loss) ..................................           $ (9,071)           $ 15,955
         Shares used in net income per common share - basic .             37,801              34,290
         Effect of dilutive securities:
           Employee and director stock options ..............                 --               1,698
                                                                        --------            --------
         Shares used in net income per common share - diluted             37,801              35,988
                                                                        ========            ========
         Net income (loss) per common share - basic .........           $  (0.24)           $   0.47
                                                                        ========            ========
         Net income (loss) per common share - diluted .......           $  (0.24)           $   0.44
                                                                        ========            ========





                                                                       Nine Months Ended September 30,
                                                                          2001                2000
                                                                          ----                ----
                                                                                      
         Net income (loss) ..................................           $(15,358)           $ 42,363
         Shares used in net income per common share - basic .             37,364              33,969
         Effect of dilutive securities:
           Employee and director stock options ..............                 --               1,673
                                                                        --------            --------
         Shares used in net income per common share - diluted             37,364              35,642
                                                                        ========            ========
         Net income (loss) per common share - basic .........           $  (0.41)           $   1.25
                                                                        ========            ========
         Net income (loss) per common share - diluted .......           $  (0.41)           $   1.19
                                                                        ========            ========


         For purposes of computing diluted earnings per share, weighted average
         common share equivalents do not include stock options with an exercise
         price greater than the average market price of the common shares during
         the period. Options to purchase 464,117 and 173,571 shares of common
         stock which were outstanding during the three and nine months ended
         September 30, 2000, respectively, were not included in the calculation
         of diluted net income per common share because the option price was
         greater than the average market price of the common shares during the
         period. All options outstanding during the three and nine months ended
         September 30, 2001 are excluded from the calculation of diluted net
         income per common share because their inclusion would be anti-dilutive.
         There were options to purchase approximately 5,069,335 shares of the
         Company's common stock outstanding as of September 30, 2001.

                              MKS INSTRUMENTS, INC.
            NOTES TO CONSOLIDATED FINANCIAL STATEMENTS - (Continued)
                  (Tables in thousands, except per share data)

6)       Inventories

         Inventories consist of the following:



                                                                          September 30,          December 31,
                                                                               2001                  2000
                                                                               ----                  ----
                                                                                           
         Raw material ...........................................           $ 26,399            $ 23,765
         Work in process ........................................             18,638              20,856
         Finished goods .........................................             25,511              24,544
                                                                             -------             -------
                                                                            $ 70,548            $ 69,165
                                                                            ========            ========


7)       Stockholders' Equity

         Total comprehensive income (loss) was as follows:




                                                                          Three Months Ended September 30,
                                                                              2001                2000
                                                                              ----                ----
                                                                                          
         Net income (loss) ......................................           $ (9,071)           $ 15,955
         Other comprehensive loss, net of taxes:
             Changes in value of financial instruments designated
               as hedges of currency and interest rate exposures                (799)                 95
             Foreign currency translation adjustment ............                987                (405)
             Unrealized loss on investments .....................                 (1)               (384)
                                                                            --------            --------
         Other comprehensive income (loss), net of taxes ........                187                (694)
                                                                            --------            --------
         Total comprehensive income (loss) ......................           $ (8,884)           $ 15,261
                                                                            ========            ========





                                                                           Nine Months Ended September 30,
                                                                              2001                2000
                                                                              ----                ----
                                                                                          
         Net income (loss) ......................................           $(15,358)           $ 42,363
         Other comprehensive loss, net of taxes:
             Changes in value of financial instruments designated
               as hedges of currency and interest rate exposures                (186)                408
             Foreign currency translation adjustment ............                 22                (779)
             Unrealized loss on investments .....................               (315)               (594)
                                                                            --------            --------
         Other comprehensive loss, net of taxes .................               (479)               (965)
                                                                            --------            --------
         Total comprehensive income (loss) ......................           $(15,837)           $ 41,398
                                                                            ========            ========


8)       Segment Information and Significant Customer

         Segment information for the three months ended September 30, 2001 and
         2000 was as follows:



                                                       North America        Far East       Europe           Total
                                                       -------------        --------       ------           -----
                                                                                              
          Net sales to unaffiliated customers 2001       $ 33,537           $11,082        $ 8,582        $ 53,201
                                              2000         93,340            17,719         10,710         121,769

                       Intersegment net sales 2001         10,858               169            326          11,353
                                              2000         18,759               805            391          19,955

                Income (loss) from operations 2001        (15,011)              865            445         (13,701)
                                              2000         20,036             1,691          2,690          24,417


                              MKS INSTRUMENTS, INC.
            NOTES TO CONSOLIDATED FINANCIAL STATEMENTS - (Continued)
                  (Tables in thousands, except per share data)

         Segment information for the nine months ended September 30, 2001 and
         2000 was as follows:



                                                      North America        Far East       Europe           Total
                                                      -------------        --------       ------           -----
                                                                                             
         Net sales to unaffiliated customers 2001       $163,733           $40,885        $32,127        $236,745
                                             2000        250,772            47,839         28,083         326,694

         Intersegment net sales              2001         39,265               857          1,041          41,163
                                             2000         48,295             1,454          1,010          50,759

         Income (loss) from operations       2001        (29,793)            4,212          4,903         (20,678)
                                             2000         55,929             4,061          5,208          65,198


         The Company had one customer comprising 14% and 31% of net sales for
         the three months ended September 30, 2001 and 2000, respectively, and
         19% and 31% for the nine months ended September 30, 2001 and 2000,
         respectively.

9)       Acquisitions and Disposal of Assets

         On April 27, 2001 (the date of purchase), MKS completed its acquisition
         of On-Line Technologies, Inc. ("On-Line"), a supplier of measurement
         and control products used for gas analysis, wafer metrology and process
         control. The acquisition has been accounted for under the purchase
         method of accounting. The purchase price was approximately $23,829,000
         and consisted of approximately 660,000 shares of MKS common stock
         valued at approximately $12,110,000, cash payments of $6,295,000,
         assumption of On-Line debt of approximately $4,728,000 and transaction
         expenses of approximately $696,000. The purchase price was allocated to
         the assets acquired based upon their estimated fair values and resulted
         in an allocation of approximately $16,050,000 to goodwill. The results
         of operations are included in the Company's consolidated statement of
         income (loss) as of and since the date of the purchase. The allocation
         of the purchase price was as follows:



                                                                                                     
         Fair value of tangible assets and liabilities assumed ...................................      $   (971)
         In-process research and development .....................................................         2,340
         Current technology ......................................................................         4,710
         Other intangibles .......................................................................         1,700
         Goodwill ................................................................................        16,050
                                                                                                        --------
                                                                                                        $ 23,829
                                                                                                        ========


         The amounts allocated to current technology, other intangibles, and
         goodwill are being amortized using the straight-line method over their
         respective estimated useful lives, which range from 5 to 7 years.

         In connection with the acquisition of On-Line, the Company obtained an
         appraisal from an independent appraiser of the fair value of its
         intangible assets. This appraisal valued purchased in-process research
         and development ("IPR&D") of various projects for the development of
         new products and technologies at approximately $2,340,000. Because the
         technological feasibility of products under development had not been
         established and no future alternative uses existed, the purchased IPR&D
         was written off during the quarter ended June 30, 2001. The value of
         the purchased IPR&D was determined using the income approach, which
         discounts expected future cash flows from projects under development to
         their net present value. Each project was analyzed to determine the
         technological innovations included; the utilization of core technology;
         the complexity, cost and time to complete development; any alternative
         future use or current technological feasibility; and the stage of
         completion. The cash flows derived from the in-process technology
         projects were discounted at a rate of 25%. The Company believes

                              MKS INSTRUMENTS, INC.
            NOTES TO CONSOLIDATED FINANCIAL STATEMENTS - (Continued)
                  (Tables in thousands, except per share data)

         this rate was appropriate given the risks associated with the
         technologies for which commercial feasibility had not been established.
         The percentage of completion for each in-process project was determined
         by identifying the elapsed time invested in the project as a ratio of
         the total time required to bring the project to technical and
         commercial feasibility. The percentage of completion for in-process
         projects acquired ranged from 55% to 65%, based on management's
         estimates of tasks completed and the tasks to be completed to bring the
         projects to technological and commercial feasibility. As of September
         30, 2001, the actual development timelines and costs were in line with
         management's estimates.

         Development of in-process technology remains a substantial risk to the
         Company due to a variety of factors including the remaining effort to
         achieve technological feasibility, rapidly changing customer
         requirements and competitive threats from other companies and
         technologies.

         The following unaudited pro forma information presents a summary of the
         historical results of operations of the Company as if the On-Line
         acquisition had occurred at the beginning of each period.



                                                     Three months ended                        Nine months ended
                                                        September 30,                            September 30,
                                                  2001                 2000                2001                 2000
                                              -----------          -----------         -----------          -----------
                                                                                                
         Net sales ..................         $    53,201          $   123,080         $   237,965          $   332,036
         Net income (loss) ..........         $    (9,071)         $    15,898         $   (14,969)         $    41,706

         Net income (loss) per share:
            Basic ...................         $     (0.24)         $      0.45         $     (0.39)         $      1.20
            Diluted .................         $     (0.24)         $      0.43         $     (0.39)         $      1.15


         The unaudited pro forma results for the nine months ended September 30,
         2001 excludes approximately $6.4 million of non-recurring charges
         directly related to the transaction that were incurred by On-Line prior
         to the date of the acquisition. Additionally, the charge for purchased
         IPR&D was not included in the unaudited pro forma results, because it
         was non-recurring and directly related to the transaction.

         These unaudited pro forma results have been prepared for comparative
         purposes only and do not purport to be indicative of the results of
         operations which actually would have resulted had the acquisition
         occurred at the beginning of the period, or which may result in the
         future.

         In August 2001, the Company sold its Nimbus System product group and
         granted a non-exclusive license of the technology of its PlasmaQuest
         System product group, for approximately $9.0 million, consisting
         primarily of approximately $4.7 million in cash and $3.9 million in a
         note receivable. The note receivable matures August 7, 2004, bears an
         annual interest rate of 9.0% and is included in other assets. The loss
         on the transaction was $1,246,000 before taxes, $998,000 net of the
         related tax benefit, and is included in other income (expense).

10)      Goodwill Impairment Charge

         In August 1999, ASTeX purchased Shamrock product group for
         approximately $6.4 million in cash. The costs of the acquisition were
         allocated on the basis of the estimated fair market value of the assets
         acquired at that time, and resulted in an allocation of $4,463,000 to
         goodwill.

         When the Company acquired the Shamrock product line, it was expected
         that sales of the existing system design and development of new system
         designs would generate future revenues. Since the acquisition, the
         Company has provided potential customers with purchase quotations for
         Shamrock systems, including a significant quotation to a potential
         customer in January 2001 for the sale of several systems. The customer
         did not purchase the systems, and the quotation expired in March 2001.
         The Company has been unsuccessful in selling any systems of the product
         line since the acquisition and, with the expiration of the significant
         quote in March 2001, believes that future Shamrock system sales will
         not be sufficient to recover the carrying value of the goodwill.


                              MKS INSTRUMENTS, INC.
            NOTES TO CONSOLIDATED FINANCIAL STATEMENTS - (Continued)
                  (Tables in thousands, except per share data)

         Additionally, the Company has no current plans for future development
         of new system designs. Consequently, the Company believed that the
         carrying amount of the Shamrock related goodwill was impaired. To
         measure the impairment, the Company performed a cash flow analysis for
         the product group and determined that the estimated future cash flows
         of the group would be insignificant. As a result, the Company wrote-off
         the carrying value of the related goodwill of approximately $3,720,000
         in the quarter ended March 31, 2001.

11)      Merger Costs

         On January 26, 2001 MKS completed its acquisition of ASTeX in a
         transaction accounted for under the pooling of interests method of
         accounting. Under the pooling of interests method of accounting, fees
         and expenses related to the merger are expensed in the period of the
         merger. During the three months ended March 31, 2001, MKS expensed
         approximately $7.7 million of merger related expenses, consisting of
         $6.9 million of investment banking, legal, accounting, printing and
         other professional fees, and $0.8 million of regulatory and other
         costs.

12)      Subsequent Event

         On October 30, 2001 the Company entered into a definitive merger
         agreement to acquire the ENI division ("ENI") of Emerson Electric Co.
         based in Rochester, New York. ENI designs, develops and manufactures
         solid-state radio frequency (RF) and direct current (DC) plasma power
         supplies, matching networks and instrumentation for the semiconductor
         and thin-film processing industries.

         Under the terms of the agreement, the Company will issue 12 million
         shares of common stock to Emerson Electric Co. in exchange for the
         businesses and assets of ENI. The merger is subject to the approval of
         MKS stockholders, regulatory approval and other customary closing
         conditions.

                              MKS INSTRUMENTS, INC.
           MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION
                            AND RESULTS OF OPERATIONS

ITEM 2.

This Quarterly Report on Form 10-Q contains a number of statements, including,
without limitation, statements relating to MKS' beliefs, expectations and plans
which are forward-looking statements, as are statements that certain actions,
conditions or circumstances will continue. Such statements are based upon
management's current expectations and are subject to a number of factors and
uncertainties. Information contained in these forward-looking statements is
inherently uncertain and actual performance and results may differ materially
due to many important factors. See "Factors That May Affect Future Results" for
some, but not all, factors that could cause actual results to differ materially
from any forward-looking statements made by MKS. The terms "MKS", the "Company",
"we", "us" and "our" refer to MKS Instruments, Inc. and its subsidiaries,
including Applied Science and Technology, Inc.

On January 26, 2001 MKS completed its acquisition of ASTeX in a transaction
accounted for under the pooling of interests method of accounting. Because the
fiscal years for MKS and ASTeX differ, the periods combined for the purposes of
the consolidated financial statements for the three and nine months ended
September 30, 2000 were as follows:



                              MKS                                             ASTeX
                              ---                                             -----
                                                         
         Three and nine months ended September 30, 2000     Three and nine months ended March 25, 2000


On April 27, 2001 (the effective date of purchase) MKS completed its acquisition
of On-Line Technologies, Inc., a supplier of measurement and control products
used for gas analysis, wafer metrology and process control. The acquisition has
been accounted for under the purchase method of accounting. The purchase price
was approximately $23,829,000 and consisted of approximately 660,000 shares of
MKS common stock valued at approximately $12,110,000, cash payments of
$6,295,000, assumption of On-Line debt of approximately $4,728,000 and
transaction expenses of approximately $696,000. Accordingly, the estimated fair
value of assets acquired and liabilities assumed were included in the Company's
consolidated balance sheet as of the effective date of the purchase. The results
of operations are included in the Company's consolidated statement of income
(loss) as of and since the effective date of the purchase.

MKS develops, manufactures and supplies gas measurement, control and analysis
products, reactive gas generator and power delivery products used in
semiconductor manufacturing and other advanced thin-film manufacturing
processes. We estimate that during 2000 approximately 76% of our net sales were
to semiconductor capital equipment manufacturers and semiconductor device
manufacturers. The following table sets forth for the periods indicated the
percentage of total net sales of certain line items included in MKS consolidated
statement of income data.



                                                                            Three months ended                Nine months ended
                                                                               September 30,                    September 30,
                                                                           2001             2000            2001             2000
                                                                           ----             ----            ----             ----
                                                                                                               
         Net sales .............................................          100.0%           100.0%          100.0%           100.0%
         Cost of sales .........................................           69.7             55.3            64.1             55.7
                                                                         ------           ------          ------           ------
         Gross profit ..........................................           30.3             44.7            35.9             44.3
         Research and development ..............................           17.5              8.0            12.6              8.0
         Selling, general and administrative ...................           32.8             15.0            22.9             15.4
         Amortization of goodwill and acquired intangible assets            5.7              1.4             3.4              0.9
         Goodwill impairment charge ............................             --               --             1.6               --
         Merger expenses .......................................             --               --             3.2               --
         In-process research and development ...................             --              0.3             1.0              0.1
                                                                         ------           ------          ------           ------
         Income (loss) from operations .........................          (25.7)            20.0            (8.8)            19.9
         Interest income, net ..................................            1.4              0.8             1.4              0.8
         Other expense, net ....................................            2.3               --             0.5              0.1
                                                                         ------           ------          ------           ------
         Income (loss) before income taxes .....................          (26.6)            20.8            (7.9)            20.6
         Provision (benefit) for income taxes ..................           (9.6)             7.8            (1.4)             7.7
                                                                         ------           ------          ------           ------
         Net income (loss) .....................................          (17.0)%           13.0%           (6.5)%           12.9%
                                                                         ======           ======          ======           ======


Results of Operations

         Net Sales. Net sales decreased 56.3% to $53.2 million for the three
months ended September 30, 2001 from $121.8 million for the three months ended
September 30, 2000. International net sales were approximately $19.7 million for
the three months ended September 30, 2001 or 37.0% of net sales and $28.4
million for the same period of 2000 or 23.3% of net sales. Net sales decreased
27.5% to $236.7 million for the nine months ended September 30, 2001 from $326.7
million for the same period of 2000. International net sales were approximately
$73.0 million for the nine months ended September 30, 2001 or 30.8% of net sales
and $75.9 million for the same period of 2000 or 23.2% of net sales. The
decrease in net sales is due to a worldwide slowdown in demand for
semiconductors during 2001 which resulted in a decline in demand for the
Company's products from the Company's semiconductor capital equipment
manufacturers and semiconductor device manufacturer customers.

         Gross Profit. Gross profit as a percentage of net sales decreased to
30.3% for the three months ended September 30, 2001 from 44.7% for the three
months ended September 30, 2000. Gross profit as a percentage of net sales
decreased to 35.9% for the nine months ended September 30, 2001 from 44.3% for
the same period of 2000. The decrease was primarily due to lower absorption of
manufacturing overhead costs. Additionally, gross margin for the nine months
ended September 30, 2001 was negatively effected by a $2.6 million write-off of
obsolete and excess inventory in the second quarter of 2001. This write-off was
significantly higher than normal and was primarily caused by a significant
reduction in demand, including reduced demand for older technology products.

         Research and Development. Research and development expense decreased
4.4% to $9.3 million or 17.5% of net sales for the three months ended September
30, 2001 from $9.7 million or 8.0% of net sales for the three months ended
September 30, 2000. The decrease was primarily due to decreased purchased
services. Research and development expense increased 15.0% to $29.9 million or
12.6% of net sales for the nine months ended September 30, 2001 from $26.0
million or 8.0% of net sales for the same period of 2000. The increase was
primarily due to increased compensation expense.

         Selling, General and Administrative. Selling, general and
administrative expenses decreased 4.4% to $17.5 million or 32.8% of net sales
for the three months ended September 30, 2001 from $18.3 million or 15.0% of net
sales for the three months ended September 30, 2000. The decrease was due
primarily to decreased purchased services and compensation expense. Selling,
general and administrative expenses increased 7.5% to $54.1 million or 22.9% of
net sales for the nine months ended September 30, 2001 from $50.3 million or
15.4% of net sales for the same period of 2000. The increase was due primarily
to increased professional fees of $2.4 million, compensation expense of $0.3
million related to the earnout from the Spectra acquisition, and other selling,
general, and administrative expenses.

         Amortization of Goodwill and Acquired Intangible Assets. Amortization
of goodwill and acquired intangible assets of $3.0 million and $8.0 million for
the three and nine months ended September 30, 2001, respectively, represents the
amortization of goodwill and other intangibles resulting from the acquisitions
completed by MKS.

         Goodwill Impairment Charge. In August 1999, ASTeX purchased the
Shamrock product group for approximately $6.4 million in cash. The costs of the
acquisition were allocated on the basis of the estimated fair market value of
the assets acquired at that time, and resulted in an allocation of $4,463,000 to
goodwill.

         When the Company acquired the Shamrock product line, it was expected
that sales of the existing system design and development of new system designs
would generate future revenues. Since the acquisition, the Company has provided
potential customers with purchase quotations for Shamrock systems, including a
significant quotation to a potential customer in January 2001 for the sale of
several systems. The customer did not purchase the systems, and the quotation
expired in March 2001. The Company has been unsuccessful in selling any systems
of the product line since the acquisition and, with the expiration of the
significant quote in March 2001, believes that future Shamrock system sales will
not be sufficient to recover the carrying value of the goodwill. Additionally,
the Company has no current plans for future development of new system designs.
Consequently, the Company believed that the carrying amount of the Shamrock
related goodwill was impaired. To measure the impairment, the Company performed
a cash flow analysis for the product group and determined that the estimated
future cash flows of the group would be insignificant. As a result, the Company
wrote-off the carrying value of the related goodwill of approximately $3,720,000
in the quarter ended March 31, 2001.

         Merger Costs. On January 26, 2001 MKS completed its acquisition of
ASTeX in a transaction accounted for under the pooling of interests method of
accounting. Under the pooling of interests method of accounting, fees and
expenses related to the merger are expensed in the period of the merger. During
the nine months ended September 30, 2001, MKS expensed approximately $7.7
million of merger related expenses, consisting of $6.9 million of investment
banking, legal, accounting, printing and other professional fees, $0.8 million
of regulatory and other costs.

         Purchase of In-process Technology. In April 2001, the Company acquired
On-Line in a transaction accounted for as a purchase. The purchase price was
allocated to the assets acquired, including intangible assets, based on their
estimated fair values. The intangible assets include approximately $2.3 million
for acquired in-process technology for projects that did not have future
alternative uses. The value of the purchased in-process technology was
determined using the income approach, which discounts expected future cash flows
from projects under development to their net present value. Each project was
analyzed to determine the technological innovations included; the utilization of
core technology; the complexity, cost and time to complete development; any
alternative future use or current technological feasibility; and the stage of
completion. At the date of the acquisition, the development of these projects
had not yet reached technological feasibility, and the technology in progress
had no alternative future uses. Accordingly, these costs were expensed in the
second quarter of 2001.

         Interest Income (Expense), Net. During the three and nine months ended
September 30, 2001, the Company generated net interest income of $0.8 million
and $3.2 million, respectively, primarily from the invested net proceeds of its
common stock offerings, offset by interest expense on outstanding debt.

         Other Income (Expense), Net. In August 2001, the Company sold its
Nimbus System product group and granted a non-exclusive license of the
technology of its PlasmaQuest System product group, for approximately
$9,000,000. The loss on the transaction was $1,246,000.

         Provision (Benefit) for Income Taxes. The effective tax rates for the
three and nine months ended September 30, 2001 were 35.9% and 18.0%,
respectively, resulting in an income tax benefit of $5.1 million and $3.4
million, respectively. The changes in effective tax rates for the three and nine
months ended September 30, 2001 as compared to the effective tax rates for the
three and nine months ended September 30, 2000 were primarily due to
non-deductible charges associated with acquisitions made in 2001.

LIQUIDITY AND CAPITAL RESOURCES

The Company has financed its operations and capital requirements through a
combination of cash provided by operations, long-term real estate financing,
capital lease financing and short-term lines of credit. On April 5, 1999, MKS
completed the initial public offering of its Common Stock. In connection with
this offering and the exercise of an over-allotment option by the underwriters,
MKS sold 6,375,000 shares of Common Stock at a price of $14.00 per share. The
net proceeds to MKS were approximately $82,000,000 and were received in the
second quarter of 1999. Underwriting discounts and commissions were
approximately $6,200,000, and other offering costs were approximately
$1,000,000. On April 5, 1999, MKS distributed $40,000,000, which was the
estimated amount of its undistributed S Corporation earnings as of the day prior
to the closing of the offering.

On March 30, 2000, ASTeX completed the registration and sale of 1,917,250 shares
of common stock at $40.42 per share. The net proceeds from the offering were
approximately $73.2 million.

On March 5, 1999, ASTeX completed the registration and sale of 1,533,800 shares
of common stock at $14.34 per share. On April 6, 1999, the underwriters
exercised their over-allotment option to purchase an additional 230,070 shares
of common stock. The net proceeds from the offering were approximately $23.8
million.

In 1998, ASTeX announced that it had met the requirements for the redemption of
redeemable warrants issued in connection with the ASTeX initial public offering
and called the warrants for redemption. 2,082,451 redeemable warrants and
133,088 underwriter warrants were converted into 1,297,147 shares of common
stock. The net proceeds were $15,234,000.

Operations provided cash of $23.2 million for the nine months ended September
30, 2001. This cash flow was impacted by the net loss, depreciation and
amortization, the goodwill impairment charge and changes in the levels of
accounts payable, accrued expenses, and accounts receivable. Investing
activities utilized cash of $22.7 million for the nine months ended September
30, 2001 primarily from the purchases of On-Line and property, plant, and
equipment. Financing activities utilized cash of $2.3 million, primarily from
payments on short-term borrowings offset by proceeds from employees exercising
stock options.

Working capital was $215 million as of September 30, 2001, a decrease of $21.9
million from December 31, 2000. The decrease in working capital was primarily
due to decreased trade accounts receivable, net. MKS entered into a new credit
agreement on July 31, 2001 whereby the Company has a combined $40.0 million line
of credit with two banks all of which is available. The credit agreement expires
on July 31, 2002.

The Company believes that its working capital, together with the cash
anticipated to be generated from operations and funds available from existing
credit facilities, will be sufficient to satisfy its estimated working capital
and planned capital expenditure requirements through at least the next 12
months.

                     FACTORS THAT MAY AFFECT FUTURE RESULTS

MKS believes that this document contains "forward-looking statements" within the
meaning of the Private Securities Litigation Reform Act of 1995. These
statements are subject to risks and uncertainties and are based on the beliefs
and assumptions of management of MKS, based on information currently available
to MKS' management. Use of words such as "believes," "expects," "anticipates,"
"intends," "plans," "estimates," "should," "likely" or similar expressions,
indicate a forward-looking statement. Forward-looking statements involve risks,
uncertainties and assumptions. Certain of the information contained in this
Quarterly Report on Form 10-Q consists of forward-looking statements. Important
factors that could cause actual results to differ materially from the
forward-looking statements include the following:

MKS' BUSINESS DEPENDS SUBSTANTIALLY ON CAPITAL SPENDING IN THE SEMICONDUCTOR
INDUSTRY WHICH IS CHARACTERIZED BY PERIODIC FLUCTUATIONS THAT MAY CAUSE A
REDUCTION IN DEMAND FOR MKS' PRODUCTS.

MKS estimates that approximately 76% of its sales in 2000 were to semiconductor
capital equipment manufacturers and semiconductor device manufacturers, and it
expects that sales to such customers will continue to account for a substantial
majority of its sales. MKS' business depends upon the capital expenditures of
semiconductor device manufacturers, which in turn depend upon the demand for
semiconductors. Periodic reductions in demand for the products manufactured by
semiconductor capital equipment manufacturers and semiconductor device
manufacturers may adversely affect MKS' business, financial condition and
results of operations. Historically, the semiconductor market has been highly
cyclical and has experienced periods of overcapacity, resulting in significantly
reduced demand for capital equipment. For example, in 1996 and 1998, the
semiconductor capital equipment industry experienced significant declines, which
caused a number of MKS customers to reduce their orders. More recently, in 2001,
MKS has experienced a significant reduction in demand from OEM customers, and
lower gross margins due to reduced absorption of manufacturing overhead at the
lower revenue levels. In addition, many semiconductor manufacturers have
operations and customers in Asia, a region which in recent years has experienced
serious economic problems including currency devaluations, debt defaults, lack
of liquidity and recessions. MKS cannot be certain that semiconductor downturns
will not recur. A decline in the level of orders as a result of any current and
future downturn or slowdown in the semiconductor capital equipment industry
could have a material adverse effect on MKS' business, financial condition and
results of operations.

MKS' QUARTERLY OPERATING RESULTS HAVE VARIED, AND ARE LIKELY TO CONTINUE TO VARY
SIGNIFICANTLY. THIS MAY RESULT IN VOLATILITY IN THE MARKET PRICE FOR MKS'
SHARES.

A substantial portion of MKS' shipments occur shortly after an order is received
and therefore MKS operates with a low level of backlog. As a result, a decrease
in demand for MKS' products from one or more customers could occur with limited
advance notice and could have a material adverse effect on MKS' results of
operations in any particular period. A significant percentage of MKS' expenses
are relatively fixed and based in part on expectations of future net sales. The
inability to adjust spending quickly enough to compensate for any shortfall
would magnify the adverse impact of a shortfall in net sales on MKS' results of
operations. Factors that could cause fluctuations in MKS' net sales include:

- -        the timing of the receipt of orders from major customers;

- -        shipment delays;

- -        disruption in sources of supply;

- -        seasonal variations of capital spending by customers;

- -        production capacity constraints; and

- -        specific features requested by customers.

For example, MKS was in the process of increasing its production capacity when
the semiconductor capital equipment market began to experience a significant
downturn in 1996. This downturn had a material adverse effect on MKS' operating
results in the second half of 1996 and the first half of 1997. After an increase
in business in the latter half of 1997, the market experienced another downturn
in 1998, which had a material adverse effect on MKS' 1998 and first quarter 1999
operating results. More recently, the semiconductor capital equipment market has
experienced a significant downturn during 2001. As a result, MKS has experienced
a reduction in demand from OEM customers in 2001, which has had a material
adverse effect on MKS' operating results. As a result of the factors discussed
above, it is likely that MKS will in the future experience quarterly or annual
fluctuations and that, in one or more future quarters, its operating results
will fall below the expectations of public market analysts or investors. In any
such event, the price of MKS' common stock could decline significantly.

THE LOSS OF NET SALES TO ANY ONE OF MKS' MAJOR CUSTOMERS WOULD LIKELY HAVE A
MATERIAL ADVERSE EFFECT ON MKS.

MKS' five largest customers accounted for approximately 45% of its net sales in
2000, 39% of its net sales in 1999 and 34% of its net sales in 1998. The loss of
a major customer or any reduction in orders by these customers, including
reductions due to market or competitive conditions, would likely have a material
adverse effect on MKS' business, financial condition and results of operations.
During 2000 and 1999, one customer, Applied Materials, accounted for
approximately 30% and 29%, respectively, of MKS' net sales. MKS' purchase
contract with Applied Materials expires in 2004. None of MKS' significant
customers, including Applied Materials, has entered into an agreement requiring
it to purchase any minimum quantity of MKS' products. The demand for MKS'
products from its semiconductor capital equipment customers depends in part on
orders received by them from their semiconductor device manufacturer customers.

Attempts to lessen the adverse effect of any loss or reduction through the rapid
addition of new customers could be difficult because prospective customers
typically require lengthy qualification periods prior to placing volume orders
with a new supplier. MKS' future success will continue to depend upon:

- -        its ability to maintain relationships with existing key customers;

- -        its ability to attract new customers; and

- -        the success of its customers in creating demand for their capital
         equipment products which incorporate MKS's products.

AS PART OF MKS' BUSINESS STRATEGY, MKS HAS ENTERED INTO AND MAY ENTER INTO OR
SEEK TO ENTER INTO BUSINESS COMBINATIONS AND ACQUISITIONS THAT MAY BE DIFFICULT
TO INTEGRATE, DISRUPT ITS BUSINESS, DILUTE STOCKHOLDER VALUE OR DIVERT
MANAGEMENT ATTENTION.

MKS acquired Compact Instrument Technology ("Compact Instrument") in March 2000,
Telvac Engineering, Ltd. ("Telvac") in May 2000, Spectra Instruments, Inc.
("Spectra") in July 2000, D.I.P., Inc. ("D.I.P.") in September 2000, ASTeX in
January 2001, On-Line in April 2001, and entered into a definitive merger
agreement to acquire the ENI division ("ENI") of Emerson Electric Co. in October
2001. As a part of its business strategy, MKS may enter into additional business
combinations and acquisitions. Acquisitions are typically accompanied by a
number of risks, including the difficulty of integrating the operations and
personnel of the acquired companies, the potential disruption of MKS' ongoing
business and distraction of management, expenses related to the acquisition and
potential unknown liabilities associated with acquired businesses.

If MKS is not successful in completing acquisitions that it may pursue in the
future, it may be required to reevaluate its growth strategy, and MKS may have
incurred substantial expenses and devoted significant management time and
resources in seeking to complete proposed acquisitions that will not generate
benefits for it.

In addition, with future acquisitions, MKS could use substantial portions of its
available cash as all or a portion of the purchase price. MKS could also issue
additional securities as consideration for these acquisitions, which could cause
significant stockholder dilution. MKS' acquisitions of Compact Instrument,
Telvac, Spectra, D.I.P., ASTeX, On-Line, and ENI and any future acquisitions may
not ultimately help MKS achieve its strategic goals and may pose other risks to
MKS.

AN INABILITY TO CONVINCE SEMICONDUCTOR DEVICE MANUFACTURERS TO SPECIFY THE USE
OF MKS' PRODUCTS TO MKS' CUSTOMERS, WHO ARE SEMICONDUCTOR CAPITAL EQUIPMENT
MANUFACTURERS, WOULD WEAKEN MKS' COMPETITIVE POSITION.

The markets for MKS' products are highly competitive. Its competitive success
often depends upon factors outside of its control. For example, in some cases,
particularly with respect to mass flow controllers, semiconductor device
manufacturers may direct semiconductor capital equipment manufacturers to use a
specified supplier's product in their equipment. Accordingly, for such products,
MKS' success will depend in part on its ability to have semiconductor device
manufacturers specify that MKS' products be used at their semiconductor
fabrication facilities. In addition, MKS may encounter difficulties in changing
established relationships of competitors that already have a large installed
base of products within such semiconductor fabrication facilities.

IF MKS' PRODUCTS ARE NOT DESIGNED INTO SUCCESSIVE NEW GENERATIONS OF ITS
CUSTOMERS' PRODUCTS, MKS WILL LOSE SIGNIFICANT NET SALES DURING THE LIFESPAN OF
THOSE PRODUCTS.

New products designed by semiconductor capital equipment manufacturers typically
have a lifespan of five to ten years. MKS' success depends on its products being
designed into new generations of equipment for the semiconductor industry. MKS
must develop products that are technologically current so that they are
positioned to be chosen for use in each successive new generation of
semiconductor capital equipment. If MKS products are not chosen by its
customers, MKS' net sales may be reduced during the lifespan of its customers'
products. In addition, MKS must make a significant capital investment to develop
products for its customers well before its products are introduced and before it
can be sure that it will recover its capital investment through sales to the
customers in significant volume. MKS is thus also at risk during the development
phase that its products may fail to meet its customers' technical or cost
requirements and may be replaced by a competitive product or alternative
technology solution. If that happens, MKS may be unable to recover MKS'
development costs.

THE SEMICONDUCTOR INDUSTRY IS SUBJECT TO RAPID DEMAND SHIFTS WHICH ARE DIFFICULT
TO PREDICT. AS A RESULT, MKS' INABILITY TO EXPAND ITS MANUFACTURING CAPACITY IN
RESPONSE TO THESE RAPID SHIFTS MAY CAUSE A REDUCTION IN ITS MARKET SHARE.

MKS' ability to increase sales of certain products depends in part upon its
ability to expand its manufacturing capacity for such products in a timely
manner. If MKS is unable to expand its manufacturing capacity on a timely basis
or to manage such expansion effectively, its customers could implement its
competitors' products and, as a result, its market share could be reduced.
Because the semiconductor industry is subject to rapid demand shifts which are
difficult to foresee, MKS may not be able to increase capacity quickly enough to
respond to a rapid increase in demand in the semiconductor industry.
Additionally, capacity expansion could increase MKS' fixed operating expenses
and if sales levels do not increase to offset the additional expense levels
associated with any such expansion, its business, financial condition and
results of operations could be materially adversely affected.

SALES TO FOREIGN MARKETS CONSTITUTE A SUBSTANTIAL PORTION OF MKS' NET SALES;
THEREFORE, MKS NET SALES AND RESULTS OF OPERATIONS COULD BE ADVERSELY AFFECTED
BY DOWNTURNS IN ECONOMIC CONDITIONS IN COUNTRIES OUTSIDE OF THE UNITED STATES.

International sales, which include sales by MKS' foreign subsidiaries, but
exclude direct export sales (which were less than 10% of MKS' total net sales),
accounted for approximately 23% of net sales in 2000, 25% of net sales in 1999
and 21% of net sales in 1998.

MKS anticipates that international sales will continue to account for a
significant portion of MKS' net sales. In addition, certain of MKS' key domestic
customers derive a significant portion of their revenues from sales in
international markets. Therefore, MKS' sales and results of operations could be
adversely affected by economic slowdowns and other risks associated with
international sales.

UNFAVORABLE CURRENCY EXCHANGE RATE FLUCTUATIONS MAY LEAD TO LOWER GROSS MARGINS,
OR MAY CAUSE MKS TO RAISE PRICES WHICH COULD RESULT IN REDUCED SALES.

Currency exchange rate fluctuations could have an adverse effect on MKS' net
sales and results of operations and MKS could experience losses with respect to
its hedging activities. Unfavorable currency fluctuations could require MKS to
increase prices to foreign customers which could result in lower net sales by
MKS to such customers. Alternatively, if MKS does not adjust the prices for its
products in response to unfavorable currency fluctuations, its results of
operations could be adversely affected. In addition, sales made by MKS' foreign
subsidiaries are denominated in the currency of the country in which these
products are sold and the currency it receives in payment for such sales could
be less valuable at the time of receipt as a result of exchange rate
fluctuations. MKS enters into forward exchange contracts and local currency
purchased options to reduce currency exposure arising from intercompany sales of
inventory. However, MKS cannot be certain that its efforts will be adequate to
protect it against significant currency fluctuations or that such efforts will
not expose it to additional exchange rate risks.

COMPETITION FOR PERSONNEL IN THE SEMICONDUCTOR AND INDUSTRIAL MANUFACTURING
INDUSTRIES IS INTENSE.

MKS' success depends to a large extent upon the efforts and abilities of a
number of key employees and officers, particularly those with expertise in the
semiconductor manufacturing and similar industrial manufacturing industries. The
loss of key employees or officers could have a material adverse effect on MKS'
business, financial condition and results of operations. MKS believes that its
future success will depend in part on its ability to attract and retain highly
skilled technical, financial, managerial and marketing personnel. Competition
for such personnel is intense, and MKS cannot be certain that it will be
successful in attracting and retaining such personnel.

MKS' PROPRIETARY TECHNOLOGY IS IMPORTANT TO THE CONTINUED SUCCESS OF ITS
BUSINESS. MKS' FAILURE TO PROTECT THIS PROPRIETARY TECHNOLOGY MAY SIGNIFICANTLY
IMPAIR MKS' COMPETITIVE POSITION.

As of September 30, 2001, MKS owned 125 U.S. patents and 62 foreign patents and
had 52 pending U.S. patent applications and 136 pending foreign patent
applications. Although MKS seeks to protect its intellectual property rights
through patents, copyrights, trade secrets and other measures, it cannot be
certain that:

- -        MKS will be able to protect its technology adequately;

- -        competitors will not be able to develop similar technology
         independently;

- -        any of MKS' pending patent applications will be issued;

- -        intellectual property laws will protect MKS' intellectual property
         rights; or

- -        third parties will not assert that MKS' products infringe patent,
         copyright or trade secrets of such parties.

PROTECTION OF MKS' INTELLECTUAL PROPERTY RIGHTS MAY RESULT IN COSTLY LITIGATION.

Litigation may be necessary in order to enforce MKS' patents, copyrights or
other intellectual property rights, to protect its trade secrets, to determine
the validity and scope of the proprietary rights of others or to defend against
claims of infringement. For example, on November 30, 2000, ASTeX brought suit in
federal district court in Delaware against Advanced Energy Industries, Inc. for
infringement of ASTeX's patent related to its Astron product. Such litigation
could result in substantial costs and diversion of resources and could have a
material adverse effect on MKS' business, financial condition and results of
operations.

THE MARKET PRICE OF MKS' COMMON STOCK HAS FLUCTUATED AND MAY CONTINUE TO
FLUCTUATE FOR REASONS OVER WHICH MKS HAS NO CONTROL.

The stock market has from time to time experienced, and is likely to continue to
experience, extreme price and volume fluctuations. Recently, prices of
securities of technology companies have been especially volatile and have often
fluctuated for reasons that are unrelated to the operating performance of the
companies. The market price of shares of MKS' common stock has fluctuated
greatly since its initial public offering and could continue to fluctuate due to
a variety of factors. In the past, companies that have experienced volatility in
the market price of their stock have been the objects of securities class action
litigation. If MKS were the object of securities class action litigation, it
could result in substantial costs and a diversion of MKS' management's attention
and resources.

MKS'S DEPENDENCE ON SOLE AND LIMITED SOURCE SUPPLIERS COULD AFFECT ITS ABILITY
TO MANUFACTURE PRODUCTS AND SYSTEMS.

MKS relies on sole and limited source suppliers for a few of its components and
subassemblies that are critical to the manufacturing of MKS's products. This
reliance involves several risks, including the following:

- -        the potential inability to obtain an adequate supply of required
         components;

- -        reduced control over pricing and timing of delivery of components; and

- -        the potential inability of its suppliers to develop technologically
         advanced products to support MKS's growth and development of new
         systems.

MKS believes that in time MKS could obtain and qualify alternative sources for
most sole and limited source parts. Seeking alternative sources of the parts
could require MKS to redesign its systems, resulting in increased costs and
likely shipping delays. MKS may be unable to redesign its systems, which could
result in further costs and shipping delays. These increased costs would
decrease MKS' profit margins if it could not pass the costs to its customers.
Further, shipping delays could damage MKS' relationships with current and
potential customers and have a material adverse effect on MKS' business and
results of operations.

MKS IS SUBJECT TO GOVERNMENTAL REGULATIONS.

MKS is subject to federal, state, local and foreign regulations, including
environmental regulations and regulations relating to the design and operation
of MKS' power supply products. MKS must ensure that these systems meet certain
safety standards, many of which vary across the countries in which MKS' systems
are used.

For example, the European Union has published directives specifically relating
to power supplies. MKS must comply with these directives in order to ship MKS'
systems into countries that are members of the European Union. MKS believes it
is in compliance with current applicable regulations, directives and standards
and has obtained all necessary permits, approvals, and authorizations to conduct
MKS' business. However, compliance with future regulations, directives and
standards could require it to modify or redesign certain systems, make capital
expenditures or incur substantial costs. If MKS does not comply with current or
future regulations, directives and standards:

- -        MKS could be subject to fines;

- -        MKS' production could be suspended; or

- -        MKS could be prohibited from offering particular systems in specified
         markets.

ONE STOCKHOLDER, ALONG WITH MEMBERS OF HIS FAMILY, CONTINUES TO HAVE A
SUBSTANTIAL INTEREST IN MKS.

As of January 31, 2001, John R. Bertucci, chairman and chief executive officer
of MKS, and members of his family, in the aggregate, beneficially owned
approximately 41.4% of MKS' outstanding common stock. As a result, these
stockholders, acting together, are able to exert substantial influence over
actions of MKS.

SOME PROVISIONS OF MKS' AMENDED AND RESTATED ARTICLES OF ORGANIZATION, MKS'
BY-LAWS AND MASSACHUSETTS LAW COULD DISCOURAGE POTENTIAL ACQUISITION PROPOSALS
AND COULD DELAY OR PREVENT A CHANGE IN CONTROL OF MKS.

Anti-takeover provisions could diminish the opportunities for stockholders to
participate in tender offers, including tender offers at a price above the then
current market value of the common stock. Such provisions may also inhibit
increases in the market price of the common stock that could result from
takeover attempts. For example, while MKS has no present plans to issue any
preferred stock, MKS' board of directors, without further stockholder approval,
may issue preferred stock that could have the effect of delaying, deterring or
preventing a change in control of MKS. The issuance of preferred stock could
adversely affect the voting power of the holders of MKS' common stock, including
the loss of voting control to others. In addition, MKS' By-Laws provide for a
classified board of directors consisting of three classes. The classified board
could also have the effect of delaying, deterring or preventing a change in
control of MKS.

         ITEM 3.  QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

Information concerning market risk is contained in the Management's Discussion
and Analysis of Financial Condition and Results of Operations contained in the
Consolidated Supplemental Financial Statements for year ended December 31, 2000,
reflecting the merger of MKS Instruments, Inc. and ASTeX, which was filed with
the Securities and Exchange Commission in MKS' Current Reports on Form 8-K on
April 20, 2001. MKS enters into local currency purchased options to reduce
currency exposure arising from intercompany sales of inventory. The potential
fair value loss for a hypothetical 10% adverse change in currency exchange rates
on MKS' local currency purchased options at September 30, 2001 would be
approximately $0.5 million. The potential loss was estimated by calculating the
fair value of the local currency purchased options at September 30, 2001 and
comparing that with those calculated using the hypothetical currency exchange
rates. There were no other material changes in MKS' exposure to market risk from
December 31, 2000.

PART II  OTHER INFORMATION

         ITEM 1.  LEGAL PROCEEDINGS

MKS is not aware of any material legal proceedings to which it or any of its
subsidiaries is a party.

         ITEM 2.  CHANGES IN SECURITIES AND USE OF PROCEEDS

         (d) Use of Proceeds from Sales of Registered Securities. The Company
         has previously provided information on Form 10-Q for the quarter ended
         September 30, 2000 relating to the use of proceeds from the sale of
         securities by the Company pursuant to the Registration Statement on
         Form S-1 (Reg. No. 333-71363) that was declared effective by the
         Securities and Exchange Commission on March 29, 1999. Cumulative use of
         net proceeds from the securities sold was $15.8 million as of September
         30, 2001. There has been no other change to the information previously
         provided.

         ITEM 3.  DEFAULTS UPON SENIOR SECURITIES

None.

         ITEM 4.  SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS

None.

         ITEM 5.  OTHER INFORMATION

None.

         ITEM 6.  EXHIBITS AND REPORTS ON FORM 8-K


         (a)      Exhibits



             Exhibit No.       Exhibit Description
             -----------       -------------------
                            
                10.37          Credit Agreement dated July 31, 2001 between Fleet National Bank as Agent and Lender, The Chase
                               Manhattan Bank as Lender, and the Registrant as Borrower

                10.38          Ninth Amendment dated July 31, 2001 to the Loan Agreement dated October 31, 1995 between
                               Fleet National Bank as Lender and the Registrant as Borrower



         (b)      Reports on Form 8-K

None.

SIGNATURE

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

                                        MKS INSTRUMENTS, INC.




November 14, 2001                       By: /s/ Ronald C. Weigner
                                            ---------------------------------
                                                Ronald C. Weigner
                                                Vice President and Chief
                                                Financial Officer
                                                (Principal Financial Officer)

EXHIBIT INDEX






     Exhibit No.        Exhibit Description
     -----------        -------------------
                     
        10.37           Credit Agreement dated July 31, 2001 between Fleet National Bank as Agent and Lender, The Chase
                        Manhattan Bank as Lender, and the Registrant as Borrower

        10.38           Ninth Amendment dated July 31, 2001 to the Loan Agreement dated October 31, 1995 between
                        Fleet National Bank as Lender and the Registrant as Borrower