SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


                                    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): April 17, 2003

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

      Massachusetts                   0-23621                   04-2277512
  (State or other juris-            (Commission               (IRS Employer
diction of incorporation)           File Number)           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


          (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 April 17, 2003, MKS Instruments, Inc. announced its financial results
for the quarter ended March 31, 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:  April 17, 2003              MKS Instruments, Inc.

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

                                  EXHIBIT INDEX



Exhibit No.                             Description
                                     
99.1                                    Press release dated April 17, 2003