SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G Under the Securities Exchange Act of 1934 Amendment # 5 Name of Issuer: KLA TENCOR CORP _____________________________________________________ Title of Class of Securities: Common Stock CUSIP Number: 482480100 1) NAME OF I.R.S. IDENTIFICATION NO. OF REPORTING PERSON The Prudential Insurance Company of America 22-1211670 2.) MEMBER OF A GROUP: (a) N/A (b) N/A 3) SEC USE ONLY: 4) PLACE OF ORGANIZATION:A mutual insurance company organized under the laws of the State of New Jersey NUMBER OF SHARES BENEFICIALLY OWNED BY REPORTING PERSON WITH: 5) Sole Voting Power:344,400See Exhibit A 6) Shared Voting Power:3,951,113See Exhibit A 7) Sole Dispositive Power:344,400See Exhibit A 8) Shared Dispositive Power:4,257,236See Exhibit A 9) AGGREGATE AMOUNT BENEFICIALLY OWNED: 4,601,636See Exhibit A 10) AGGREGATE AMOUNT IN ROW (9) EXCLUDES SHARES:Not Applicable 11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9): 5.12 See Exhibit A 12) TYPE OF REPORTING PERSON: IC, IA ITEM 1(a). NAME OF ISSUER: KLA TENCOR CORP ITEM 1(b). ADDRESS OF ISSUER'S EXECUTIVE OFFICES: KLA TENCOR CORP 160 Rio Robles San Jose, CA 95134 ITEM 2(a). NAME OF PERSON FILING: The Prudential Insurance Company of America ITEM 2(b). ADDRESS OF PRINCIPAL BUSINESS OFFICE: 751 Broad Street Newark, New Jersey 07102-3777 ITEM 2(c). CITIZENSHIP: A mutual insurance company organized under the laws of the State of New Jersey ITEM 2(d). TITLE OF CLASS OF SECURITIES: Common Stock ITEM 2(e). CUSIP NUMBER: 482480100 ITEM 3.The Person filing this statement is an Insurance Company as defined in Section 3(a) (19) of the Securities Exchange Act of 1934, and an Investment Adviser registered under Section 203 of the Investment Advisers Act of 1940. ITEM 4. OWNERSHIP: (a) Number of Shares Beneficially Owned:4,601,636 See Exhibit A (b) Percent of Class:5.12 Number (c) PowersOf Shares ------------------------------------- ------------------------------------- Sole power to vote or344,400 See Exhibit A to direct the vote Shared power to vote or3,951,113 See Exhibit A to direct the vote Sole power to dispose or344,400 See Exhibit A to direct disposition Shared power to dispose4,257,236 See Exhibit A or to direct disposition ITEM 5. OWNERSHIP OF 5% OR LESS OF A CLASS: Not Applicable ITEM 6. OWNERSHIP OF MORE THAN 5% ON BEHALF OF ANOTHER PERSON: See Exhibit A ITEM 7.IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE SECURITY BEING REPORTED ON BY THE ULTIMATE PARENT 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: By signing below, the Prudential Insurance Company of America certifies that, to the best of its knowledge and belief, the securities referred to above were acquired in the ordinary course of business and were not acquired for the purpose of and do not have the effect of changing or influencing the control of the issuer of such securities and were not acquired in connection with or as a participant in any transaction having such purpose or effect. The filing of this statement should not be construed as an admission that Prudential is, for purposes of Sections 13 or 16 of the Securities Exchange Act of 1934, the beneficial owner of such shares. SIGNATURE After reasonable inquiry and to the best of its knowledge and belief, The Prudential Insurance Company of America certifies that the information set forth in this statement is true, complete and correct. THE PRUDENTIAL INSURANCE COMPANY OF AMERICA By:Ellen McGlynn Koke Vice President Date:01/31/2000 As of:12/31/1999 Exhibit A -------------- ITEM 6. OWNERSHIP: The Prudential Insurance Company of America ('Prudential') presently holds 21,500 shares of Issuer's common stock for the benefit of its general account. In addition, Prudential may have direct or indirect voting and/or investment discretion over 4,580,136 shares which are held for its own benefit or for the benefit of its clients by its separate accounts, externally managed accounts, registered investment companies, subsidiaries and/or other affiliates. Prudential is reporting the combined holdings of these entities for the purpose of administrative convenience. These shares were acquired in the ordinary course of business, and not with the purpose or effect of changing or influencing control of the Issuer. The filing of this statement should not be construed as an admission that Prudential is, for the purposes of Sections 13 or 16 of the Securities Exchange Act of 1934, the beneficial owner of these shares.