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.