SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

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                                    FORM 8-K

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

         Date of Report (Date of earliest event reported): July 22, 2003

                              MKS Instruments, Inc.
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               (Exact name of registrant as specified in charter)

      Massachusetts                    0-23621                 04-2277512
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 (State or other juris-              (Commission              (IRS Employer
diction of incorporation)           File Number)           Identification No.)


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


        Registrant's telephone number, including area code: 978.975.2350


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          (Former name or former address, if changed since last report)

ITEM 9. REGULATION FD DISCLOSURE (INFORMATION FURNISHED PURSUANT TO ITEM 12,
"DISCLOSURE OF RESULTS OF OPERATIONS AND FINANCIAL CONDITION").

      On July 22, 2003, MKS Instruments, Inc. announced its financial results
for the quarter ended June 30, 2003. The full text of the press release issued
in connection with the announcement is attached as Exhibit 99.1 to this Current
Report on Form 8-K.

      In accordance with the procedural guidance in SEC Release No. 33-8216, the
information in this Form 8-K and the Exhibit attached hereto is being furnished
under "Item 9. Regulation FD Disclosure" rather than under "Item 12. Disclosure
of Results of Operations and Financial Condition." The information shall not be
deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934
(the "Exchange Act") or otherwise subject to the liabilities of that section,
nor shall it be deemed incorporated by reference in any filing under the
Securities Act of 1933 or the Exchange Act, except as expressly set forth by
specific reference in such a filing.

                                    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 hereunto duly authorized.

Date:  July 22, 2003               MKS Instruments, Inc.

                                   By:  /s/ Ronald C. Weigner
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                                        Ronald C. Weigner,
                                        Vice President & Chief Financial Officer

                                  EXHIBIT INDEX



Exhibit No.        Description
                
99.1               Press release dated July 22, 2003