SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 SCHEDULE 13G (RULE 13d-102) INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO RULES 13d-1(b)(c), AND (d) AND AMENDMENTS THERETO FILED PURSUANT TO RULE 13d-(2)(b) (AMENDMENT NO. 3) MKS Instruments, Inc. (Name of Issuer) Common Stock (Title of Class of Securities) 55306N 10 4 (CUSIP Number) December 31, 2002 (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate the rule pursuant to which this Schedule is filed: / / Rule 13d-1(b) / / Rule 13d-1(c) /X/ Rule 13d-1(d)
CUSIP No. 55306N 10 4 13G Page 2 of Page 6 1 NAMES OF REPORTING PERSONS. I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY) Claire R. Bertucci 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) / / (b) / / Not Applicable 3 SEC USE ONLY 4 CITIZENSHIP OR PLACE OF ORGANIZATION United States NUMBER OF SHARES 5 SOLE VOTING POWER BENEFICIALLY OWNED BY 5,453,927(1) EACH REPORTING PERSON 6 SHARED VOTING POWER WITH 0 7 SOLE DISPOSITIVE POWER 5,453,927(1) 8 SHARED DISPOSITIVE POWER 0 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 5,453,927(1) 10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES* Not Applicable 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 10.6% 12 TYPE OF REPORTING PERSON* IN * See Instructions before filling out - -------- (1) EXCLUDES, PURSUANT TO RULE 13D-4, 5,693,805 SHARES BENEFICIALLY OWNED BY JOHN R. BERTUCCI, MRS. BERTUCCI'S SPOUSE, WITH RESPECT TO WHICH MRS. BERTUCCI DISCLAIMS BENEFICIAL OWNERSHIP.
CUSIP No. 55306N 10 4 13G Page 3 of Page 6 Item 1(a). Name of Issuer: MKS Instruments, Inc. Item 1(b). Address of Issuer's Principal Executive Offices: Six Shattuck Road Andover, MA 01810 Item 2(a). Name of Person Filing: Claire R. Bertucci Item 2(b). Address of Principal Business Office or, if None, Residence: The address of the reporting persons is: c/o MKS Instruments, Inc. Six Shattuck Road Andover, MA 01810 Item 2(c). Citizenship: Mrs. Bertucci is a citizen of the United States. Item 2(d). Title of Class of Securities: Common Stock, no par value per share. Item 2(e). CUSIP Number: CUSIP No. 55306N 10 4 Item 3. If This Statement is Filed Pursuant to Rule 13d-1(b), or 13d-2(b) or (c), Check Whether the Person Filing is a: Not Applicable. (a) / / Broker or dealer registered under Section 15 of the Exchange Act. (b) / / Bank as defined in Section 3(a)(6) of the Exchange Act. (c) / / Insurance company as defined in Section 3(a)(19) of the Exchange Act. (d) / / Investment company registered under Section 8 of the Investment Company Act.
CUSIP No. 55306N 10 4 13G Page 4 of Page 6 (e) / / An investment adviser in accordance with Rule 13d-1(b)(1)(ii)(E); (f) / / An employee benefit plan or endowment fund in accordance with Rule 13d-1(b)(1)(ii)(F); (g) / / A parent holding company or control person in accordance with Rule 13d-1(b)(1)(ii)(G); (h) / / A savings association as defined in Section 3(b) of the Federal Deposit Insurance Act; (i) / / A church plan that is excluded from the definition of an investment company under Section 3(c)(14) of the Investment Company Act; (j) / / Group, in accordance with Rule 13d-1(b)(1)(ii)(J). Item 4. Ownership: The filing of this statement shall not be construed as an admission that any of the reporting persons are, for the purpose of Section 13(d) or 13(g) of the Act, the beneficial owners of any securities covered under this Statement. (a) Amount Beneficially Owned by Claire R. Bertucci 5,453,927(2) shares (b) Percent of Class: 10.6% (c) Number of Shares as to which Claire R. Bertucci has: (i) Sole power to vote or to direct the vote: 5,453,927(2) shares (ii) Shared power to vote or to direct the vote: 0 shares (iii) Sole power to dispose or to direct the disposition of: 5,453,927(2) shares (iv) Shared power to dispose or to direct the disposition of: 0 shares Item 5. Ownership of Five Percent or Less of a Class. If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than 5% of the class of securities, check the following: [ ]. - -------- (2) EXCLUDES, PURSUANT TO RULE 13D-4, 5,693,805 SHARES BENEFICIALLY OWNED BY JOHN R. BERTUCCI, MRS. BERTUCCI'S SPOUSE, WITH RESPECT TO WHICH MRS. BERTUCCI DISCLAIMS BENEFICIAL OWNERSHIP.
CUSIP No. 55306N 10 4 13G Page 5 of Page 6 Item 6. Ownership of More than Five Percent on Behalf of Another Person. Not applicable Item 7. Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company. Not applicable Item 8. Identification and Classification of Members of the Group. Not applicable Item 9. Notice of Dissolution of Group. Not applicable Item 10. Certification. Not applicable
CUSIP No. 55306N 10 4 13G Page 6 of Page 6 SIGNATURES After reasonable inquiry and to the best of the knowledge and belief of each of the undersigned, each of the undersigned hereby certifies that the information set forth in this statement is true, complete and correct. Dated: February 11, 2003 /s/ Claire R. Bertucci ------------------------------------ Claire R. Bertucci