content: <PAGE>
  
       As filed with the Securities and Exchange Commission on June 10, 2004
  
                                                        Registration No. 333- ____
  
  ================================================================================
  
                         SECURITIES AND EXCHANGE COMMISSION
                               WASHINGTON, D.C. 20549
  
                                      FORM S-8
  
                            REGISTRATION STATEMENT UNDER
                             THE SECURITIES ACT OF 1933
  
                                MKS INSTRUMENTS, INC.
               (Exact Name of Registrant as Specified in Its Charter)
  
           MASSACHUSETTS                                       04-2277512
  (State or Other Jurisdiction of                           (I.R.S. Employer
  Incorporation or Organization)                          Identification Number)
  
  90 INDUSTRIAL WAY, WILMINGTON, MASSACHUSETTS                     01887
  (Address of Principal Executive Offices)                       (Zip Code)
  
             SECOND AMENDED AND RESTATED 1997 DIRECTOR STOCK OPTION PLAN
                              (Full Title of the Plan)
  
                                  JOHN R. BERTUCCI
                        CHAIRMAN AND CHIEF EXECUTIVE OFFICER
                                MKS INSTRUMENTS, INC.
                                  90 INDUSTRIAL WAY
                                WILMINGTON, MA 01887
                       (Name and Address of Agent For Service)
  
                                   (978) 284-4000
            (Telephone Number, Including Area Code, of Agent For Service)
  
                           CALCULATION OF REGISTRATION FEE
  
  <TABLE>
  <CAPTION>
                                                        Proposed               Proposed
      Title of                                           Maximum                Maximum
  Securities to be            Amount to be         Offering Price Per          Aggregate              Amount of
     Registered              Registered(1)                Share             Offering Price        Registration Fee
  ----------------           -------------         ------------------       --------------        ----------------
  <S>                        <C>                   <C>                      <C>                   <C>
  Common
  Stock, no par
  value per share                450,000                $22.78(1)           $10,251,000(1)            $1,298.80
  </TABLE>
  
  (1) Estimated solely for the purpose of calculating the registration fee
  pursuant to Rules 457(c) and 457(h) of the Securities Act of 1933, as amended,
  and based upon the average of the high and low prices of the Registrant's Common
  Stock as reported on the Nasdaq National Market on June 9, 2004.
  
  <PAGE>
  
                       STATEMENT OF INCORPORATION BY REFERENCE
  
        Except as otherwise set forth below, this Registration Statement on Form
  S-8 incorporates by reference the contents of the Registration Statement on Form
  S-8, File No. 333-78073, relating to the Registrant's Second Amended and
  Restated 1997 Director Stock Option Plan.
  
  <PAGE>
  
                                     SIGNATURES
  
        Pursuant to the requirements of the Securities Act, the Registrant
  certifies that it has reasonable grounds to believe that it meets all of the
  requirements for filing on Form S-8 and has duly caused this Registration
  Statement to be signed on its behalf by the undersigned, thereunto duly
  authorized, in Wilmington, Massachusetts on June 2, 2004.
  
                             MKS INSTRUMENTS, INC.
  
                             By: /s/ John R. Bertucci
                                 -------------------------------------
                                 John R. Bertucci
                                 Chairman of the Board and Chief Executive Officer
  
                          POWER OF ATTORNEY AND SIGNATURES
  
        We, the undersigned officers and directors of MKS Instruments, Inc. hereby
  severally constitute and appoint John R. Bertucci, Ronald C. Weigner and Mark G.
  Borden, and each of them singly, our true and lawful attorneys with full power
  to them, and each of them singly, to sign for us and in our names in the
  capacities indicated below, the Registration Statement on Form S-8 filed
  herewith and any and all subsequent amendments to said Registration Statement,
  and generally to do all such things in our names and behalf in our capacities as
  officers and directors to enable MKS Instruments, Inc. to comply with all
  requirements of the Securities and Exchange Commission, hereby ratifying and
  confirming our signatures as they may be signed by said attorneys, or any of
  them, to said Registration Statement and any and all amendments thereto.
  
        PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT, THIS REGISTRATION
  STATEMENT HAS BEEN SIGNED BY THE FOLLOWING PERSONS IN THE CAPACITIES AND ON THE
  DATES INDICATED.
  
  <TABLE>
  <CAPTION>
          Signature                                Title                        Date
  --------------------------             --------------------------------    --------------
  <S>                                    <C>                                 <C>
  
  /s/ John R. Bertucci
  --------------------------             Chairman of the Board and Chief      June 2, 2004
  John R. Bertucci                       Executive Officer (Principal
                                         Executive Officer)
  
  
  /s/ Ronald C. Weigner
  --------------------------             Vice President and Chief             June 2, 2004
  Ronald C. Weigner                      Financial Officer (Principal
                                         Financial Officer and Principal
                                         Accounting Officer)
  
  
  /s/ Robert R. Anderson
  --------------------------             Director                             June 2, 2004
  Robert R. Anderson
  
  
  /s/ James G. Berges
  --------------------------             Director                             June 2, 2004
  James G. Berges
  
  
  /s/ Richard S. Chute
  --------------------------             Director                             June 2, 2004
  Richard S. Chute
  
  
  /s/ Hans-Jochen Kahl
  --------------------------             Director                             June 2, 2004
  Hans-Jochen Kahl
  </TABLE>
  
  <PAGE>
  
  <TABLE>
  <S>                                    <C>                                 <C>
  
  /s/ Owen W. Robbins
  -------------------------              Director                            June 2, 2004
  Owen W. Robbins
  
  
  /s/ Louis P. Valente
  -------------------------              Director                            June 2, 2004
  Louis P. Valente
  </TABLE>
  
  <PAGE>
  
                                    EXHIBIT INDEX
  
  Exhibit
  Number                          Description
  
  4.1 (1)          Restated Articles of Organization of the Registrant.
  
  4.2 (2)          Articles of Amendment.
  
  4.3 (3)          Articles of Amendment.
  
  4.4 (4)          Amended and Restated By-Laws of the Registrant.
  
  4.5 (4)          Specimen Certificate for Common Stock of the Registrant.
  
  5.1              Opinion of Wilmer Cutler Pickering Hale and Dorr LLP.
  
  23.1             Consent of Wilmer Cutler Pickering Hale and Dorr LLP (included
                   in Exhibit 5.1).
  
  23.2             Consent of PricewaterhouseCoopers LLP.
  
  24.1             Power of Attorney (included in the signature pages of this
                   Registration Statement).
  
  ------------
  
  (1)   Incorporated herein by reference from the Registrant's Registration
        Statement on Form S-4 (File No. 333-49738) filed with the Securities and
        Exchange Commission on November 13, 2000.
  
  (2)   Incorporated herein by reference from the Registrant's Quarterly Report on
        Form 10-Q (File No. 000-23621) for the quarter ended June 30, 2001.
  
  (3)   Incorporated herein by reference from the Registrant's Quarterly Report on
        Form 10-Q (File No. 000-23621) for the quarter ended June 30, 2002.
  
  (4)   Incorporated herein by reference from the Registrant's Registration
        Statement on Form S-1 (File No. 333-71363) filed with the Securities and
        Exchange Commission on January 28, 1999, as amended.
metadata_documents: [{"type": "S-8", "sequence": "1", "filename": "b50784dssv8.txt", "description": "MKS INSTRUMENTS, INC. FORM S-8", "secsgml_size_bytes": 8050}]
metadata_filer: {"company-data": {"conformed-name": "MKS INSTRUMENTS INC", "cik": "0001049502", "assigned-sic": "3823", "irs-number": "042277512", "state-of-incorporation": "MA", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-116389", "film-number": "04858745"}, "business-address": {"street1": "90 INDUSTRIAL WAY", "city": "WILMINGTON", "state": "MA", "zip": "01887", "phone": "978-284-4000"}, "mail-address": {"street1": "90 INDUSTRIAL WAY", "city": "WILMINGTON", "state": "MA", "zip": "01887"}}
text: As filed with the Securities and Exchange Commission on June 10, 2004
  
                                                        Registration No. 333- ____
  
  ================================================================================
  
                         SECURITIES AND EXCHANGE COMMISSION
                               WASHINGTON, D.C. 20549
  
                                      FORM S-8
  
                            REGISTRATION STATEMENT UNDER
                             THE SECURITIES ACT OF 1933
  
                                MKS INSTRUMENTS, INC.
               (Exact Name of Registrant as Specified in Its Charter)
  
           MASSACHUSETTS                                       04-2277512
  (State or Other Jurisdiction of                           (I.R.S. Employer
  Incorporation or Organization)                          Identification Number)
  
  90 INDUSTRIAL WAY, WILMINGTON, MASSACHUSETTS                     01887
  (Address of Principal Executive Offices)                       (Zip Code)
  
             SECOND AMENDED AND RESTATED 1997 DIRECTOR STOCK OPTION PLAN
                              (Full Title of the Plan)
  
                                  JOHN R. BERTUCCI
                        CHAIRMAN AND CHIEF EXECUTIVE OFFICER
                                MKS INSTRUMENTS, INC.
                                  90 INDUSTRIAL WAY
                                WILMINGTON, MA 01887
                       (Name and Address of Agent For Service)
  
                                   (978) 284-4000
            (Telephone Number, Including Area Code, of Agent For Service)
  
                           CALCULATION OF REGISTRATION FEE
  Proposed               Proposed
      Title of                                           Maximum                Maximum
  Securities to be            Amount to be         Offering Price Per          Aggregate              Amount of
     Registered              Registered(1)                Share             Offering Price        Registration Fee
  ----------------           -------------         ------------------       --------------        ----------------
  Common
  Stock, no par
  value per share                450,000                $22.78(1)           $10,251,000(1)            $1,298.80
  (1) Estimated solely for the purpose of calculating the registration fee
  pursuant to Rules 457(c) and 457(h) of the Securities Act of 1933, as amended,
  and based upon the average of the high and low prices of the Registrant's Common
  Stock as reported on the Nasdaq National Market on June 9, 2004.
  STATEMENT OF INCORPORATION BY REFERENCE
  
        Except as otherwise set forth below, this Registration Statement on Form
  S-8 incorporates by reference the contents of the Registration Statement on Form
  S-8, File No. 333-78073, relating to the Registrant's Second Amended and
  Restated 1997 Director Stock Option Plan.
  SIGNATURES
  
        Pursuant to the requirements of the Securities Act, the Registrant
  certifies that it has reasonable grounds to believe that it meets all of the
  requirements for filing on Form S-8 and has duly caused this Registration
  Statement to be signed on its behalf by the undersigned, thereunto duly
  authorized, in Wilmington, Massachusetts on June 2, 2004.
  
                             MKS INSTRUMENTS, INC.
  
                             By: /s/ John R. Bertucci
                                 -------------------------------------
                                 John R. Bertucci
                                 Chairman of the Board and Chief Executive Officer
  
                          POWER OF ATTORNEY AND SIGNATURES
  
        We, the undersigned officers and directors of MKS Instruments, Inc. hereby
  severally constitute and appoint John R. Bertucci, Ronald C. Weigner and Mark G.
  Borden, and each of them singly, our true and lawful attorneys with full power
  to them, and each of them singly, to sign for us and in our names in the
  capacities indicated below, the Registration Statement on Form S-8 filed
  herewith and any and all subsequent amendments to said Registration Statement,
  and generally to do all such things in our names and behalf in our capacities as
  officers and directors to enable MKS Instruments, Inc. to comply with all
  requirements of the Securities and Exchange Commission, hereby ratifying and
  confirming our signatures as they may be signed by said attorneys, or any of
  them, to said Registration Statement and any and all amendments thereto.
  
        PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT, THIS REGISTRATION
  STATEMENT HAS BEEN SIGNED BY THE FOLLOWING PERSONS IN THE CAPACITIES AND ON THE
  DATES INDICATED.
  Signature                                Title                        Date
  --------------------------             --------------------------------    --------------
  /s/ John R. Bertucci
  --------------------------             Chairman of the Board and Chief      June 2, 2004
  John R. Bertucci                       Executive Officer (Principal
                                         Executive Officer)
  
  /s/ Ronald C. Weigner
  --------------------------             Vice President and Chief             June 2, 2004
  Ronald C. Weigner                      Financial Officer (Principal
                                         Financial Officer and Principal
                                         Accounting Officer)
  
  /s/ Robert R. Anderson
  --------------------------             Director                             June 2, 2004
  Robert R. Anderson
  
  /s/ James G. Berges
  --------------------------             Director                             June 2, 2004
  James G. Berges
  
  /s/ Richard S. Chute
  --------------------------             Director                             June 2, 2004
  Richard S. Chute
  
  /s/ Hans-Jochen Kahl
  --------------------------             Director                             June 2, 2004
  Hans-Jochen Kahl
  /s/ Owen W. Robbins
  -------------------------              Director                            June 2, 2004
  Owen W. Robbins
  
  /s/ Louis P. Valente
  -------------------------              Director                            June 2, 2004
  Louis P. Valente
  EXHIBIT INDEX
  
  Exhibit
  Number                          Description
  
  4.1 (1)          Restated Articles of Organization of the Registrant.
  
  4.2 (2)          Articles of Amendment.
  
  4.3 (3)          Articles of Amendment.
  
  4.4 (4)          Amended and Restated By-Laws of the Registrant.
  
  4.5 (4)          Specimen Certificate for Common Stock of the Registrant.
  
  5.1              Opinion of Wilmer Cutler Pickering Hale and Dorr LLP.
  
  23.1             Consent of Wilmer Cutler Pickering Hale and Dorr LLP (included
                   in Exhibit 5.1).
  
  23.2             Consent of PricewaterhouseCoopers LLP.
  
  24.1             Power of Attorney (included in the signature pages of this
                   Registration Statement).
  
  ------------
  
  (1)   Incorporated herein by reference from the Registrant's Registration
        Statement on Form S-4 (File No. 333-49738) filed with the Securities and
        Exchange Commission on November 13, 2000.
  
  (2)   Incorporated herein by reference from the Registrant's Quarterly Report on
        Form 10-Q (File No. 000-23621) for the quarter ended June 30, 2001.
  
  (3)   Incorporated herein by reference from the Registrant's Quarterly Report on
        Form 10-Q (File No. 000-23621) for the quarter ended June 30, 2002.
  
  (4)   Incorporated herein by reference from the Registrant's Registration
        Statement on Form S-1 (File No. 333-71363) filed with the Securities and
        Exchange Commission on January 28, 1999, as amended.