SCHEDULE 13G

Amendment No. 3 
KLA-Tencor Corporation 
common stock 
Cusip # 482480100                

Cusip # 482480100           
Item 1:	Reporting Person - FMR Corp.
Item 4:	Commonwealth of Massachusetts
Item 5:	1,416,753 
Item 6:	0 
Item 7:	13,102,673 
Item 8:	0 
Item 9:	13,102,673 
Item 11:	14.989% 
Item 12:	    HC

Cusip # 482480100    
Item 1:	Reporting Person - Edward C. Johnson 3d 
Item 4:	United States of America
Item 5:	0 
Item 6:	0 
Item 7:	13,102,673 
Item 8:	0 
Item 9:	13,102,673 
Item 11:	14.989% 
Item 12:	IN 

Cusip # 482480100      
Item 1:	Reporting Person - Abigail P. Johnson 
Item 4:	United States of America
Item 5:	None 
Item 6:	None 
Item 7:	13,102,673 
Item 8:	None 
Item 9:	13,102,673 
Item 11:	14.989% 
Item 12:	    IN


SCHEDULE 13G - TO BE INCLUDED IN STATEMENTS
FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)


Item 1(a).	Name of Issuer:	

		KLA-Tencor Corporation 

Item 1(b).	Name of Issuer's Principal Executive Offices:

		160 Rio Robles,    
		San Jose, CA  95134  

Item 2(a).	Name of Person Filing: 

		FMR Corp.

Item 2(b).	Address or Principal Business Office or, if None, 
Residence:

		82 Devonshire Street, Boston, Massachusetts  02109

Item 2(c).	Citizenship:

		Not applicable

Item 2(d).	Title of Class of Securities:

		common stock 

Item 2(e).	CUSIP Number:  

		482480100 

Item 3.	This statement is filed pursuant to Rule 13d-1(b) or 13d-
2(b) and the person filing, FMR Corp., is a parent holding company in 
accordance with Section 240.13d-1(b)(ii)(G).  (Note:  See Item 7).

Item 4.	Ownership

	(a)	Amount Beneficially Owned:	13,102,673 

	(b)	Percent of Class:	14.989% 

	(c)	Number of shares as to which such person has:  

	(i)	sole power to vote or to direct the vote:	1,416,753 

	(ii)	shared power to vote or to direct the vote:	0 

	(iii)	sole power to dispose or to direct the disposition of:
	13,102,673 

	(iv)	shared power to dispose or to direct the disposition of:
	0 




Item 5.	Ownership of Five Percent or Less of a CommonStock.

	Not applicable.

Item 6.	Ownership of More than Five Percent on Behalf of Another 
Person.

	Various persons have the right to receive or the power to direct 
the receipt of dividends from, or the proceeds from the sale of, the 
common stock of KLA-Tencor Corporation.  No one person's interest in 
the common stock of KLA-Tencor Corporation is more than five percent of 
the total outstanding common stock.

Item 7.	Identification and Classification of the Subsidiary Which 
Acquired the Security Being Reported on By the Parent Holding Company.

	See attached Exhibit(s) A, B, and C. 

Item 8.	Identification and Classification of Members of the Group.

	Not Applicable. See attached Exhibit A. 

Item 9.	Notice of Dissolution of Group.

	Not applicable.

Item 10.	Certification.

	By signing below I certify that, to the best of my 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.

	
Signature

	After reasonable inquiry and to the best of my knowledge and 
belief, I certify that the information set forth in this Schedule 13G 
in connection with FMR Corp.'s beneficial ownership of the common stock 
of KLA-Tencor Corporation at December 31, 1998 is true, complete and 
correct. 


	February 01, 1999 
Date



	/s/Eric D. Roiter
Signature



	Eric D. Roiter	
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of FMR Corp. and its direct and indirect
	subsidiaries



SCHEDULE 13G - TO BE INCLUDED IN STATEMENTS
FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)

	Pursuant to the instructions in Item 7 of Schedule 13G, Fidelity 
Management & Research Company ("Fidelity"), 82 Devonshire Street, 
Boston, Massachusetts 02109, a wholly-owned subsidiary of FMR Corp. and 
an investment adviser registered under Section 203 of the Investment 
Advisers Act of 1940, is the beneficial owner of 11,730,120 shares or 
13.420% of the common stock outstanding of KLA-Tencor Corporation ("the 
Company") as a result of acting as investment adviser to various 
investment companies registered under Section 8 of the Investment 
Company Act of 1940, and as a result of acting as sub-adviser to 
Fidelity American Special Situations Trust ("FASST").

	FASST is a unit trust established and authorized by the 
Department of Trade and Industry under the laws of England.  The 
investment adviser of FASST is Fidelity Investment Services Limited, an 
English company and a subsidiary of Fidelity International Limited 
("FIL").

	Edward C. Johnson 3d, FMR Corp., through its control of Fidelity, 
and the funds each has sole power to dispose of the 11,654,120 shares 
owned by the Funds.

	Neither FMR Corp. nor Edward C. Johnson 3d, Chairman of FMR 
Corp., has the sole power to vote or direct the voting of the shares 
owned directly by the Fidelity Funds, which power resides with the 
Funds' Boards of Trustees.  Fidelity carries out the voting of the 
shares under written guidelines established by the Funds' Boards of 
Trustees.

	FIL, FMR Corp., through its control of Fidelity, and FASST each 
has sole power to vote and to dispose of the 76,000 shares held by 
FASST.

	Fidelity Management Trust Company, 82 Devonshire Street, Boston, 
Massachusetts 02109, a wholly-owned subsidiary of FMR Corp. and a bank 
as defined in Section 3(a)(6) of the Securities Exchange Act of 1934, 
is the beneficial owner of  1,247,153 shares or 1.426% of the common 
stock outstanding of the Company as a result of its serving as 
investment manager of the institutional account(s). 

	Edward C. Johnson 3d and FMR Corp., through its control of 
Fidelity Management Trust Company, each has sole dispositive power over 
1,247,153 shares and sole power to vote or to direct the voting of 
1,215,353 shares, and no power to vote or to direct the voting of 
31,800 shares of common stock owned by the institutional account(s) as 
reported above.

	Members of the Edward C. Johnson 3d family and trusts for their 
benefit are the predominant owners of Class B shares of common stock of 
FMR Corp., representing approximately 49% of the voting power of FMR 
Corp.  Mr. Johnson 3d owns 12.0% and Abigail Johnson owns 24.5% of the 
aggregate outstanding voting stock of FMR Corp.  Mr. Johnson 3d is 
Chairman of FMR Corp. and Abigail P. Johnson is a Director of FMR Corp.  
The Johnson family group and all other Class B shareholders have 
entered into a shareholders' voting agreement under which all Class B 
shares will be voted in accordance with the majority vote of Class B 
shares.  Accordingly, through their ownership of voting common stock 
and the execution of the shareholders' voting agreement, members of the 
Johnson family may be deemed, under the Investment Company Act of 1940, 
to form a controlling group with respect to FMR Corp.

	Fidelity International Limited, Pembroke Hall, 42 Crowlane, 
Hamilton, Bermuda, and various foreign-based subsidiaries provide 
investment advisory and management services to a number of non-U.S. 
investment companies (the "International Funds") and certain 
institutional investors.  Fidelity International Limited is the 
beneficial owner of 201,400 shares or 0.230% of the common stock 
outstanding of the Company, which includes 76,000 shares or 0.086% of 
the common stock outstanding of the company owned by FASST. Additional 
information with respect to the beneficial ownership of Fidelity 
International Limited is shown on Exhibit B, page 9
 .


SCHEDULE 13G - TO BE INCLUDED IN STATEMENTS
FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)

	Pursuant to instructions in Item 7 of Schedule 13G, this Exhibit 
has been prepared  to identify Fidelity International Limited, Pembroke 
Hall, 42 Crow Lane, Hamilton, Bermuda, a Bermudan joint stock company 
incorporated for an unlimited duration by private act of the Bermuda 
Legislature (FIL) and an investment adviser to various investment 
companies (the "International Funds") and certain institutional 
investors, as a beneficial owner of the 201,400 shares or 0.230% of the 
common stock outstanding of KLA-Tencor Corporation, which includes 
76,000 shares or 0.086% of the common stock outstanding of the company 
owned by FASST. 

	Prior to June 30, 1980, FIL was a majority-owned subsidiary of 
Fidelity Management & Research Company (Fidelity), a wholly-owned 
subsidiary of FMR Corp.  On that date, the shares of FIL held by 
Fidelity were distributed, as a dividend,  to the shareholders of FMR 
Corp.  FIL currently operates as an entity independent of FMR Corp. and 
Fidelity.  The International Funds and FIL's other clients, with the 
exception of Fidelity and an affiliated company of Fidelity, are non-
U.S. entities.

	A partnership controlled by Edward C. Johnson 3d and members of 
his family owns shares of FIL voting stock with the right to cast 
approximately 39.89% of the total votes which may be cast by all 
holders of FIL voting stock.  Mr. Johnson 3d is Chairman of FMR Corp. 
and FIL.  FMR Corp. and FIL are separate and independent corporate 
entities, and their Boards of Directors are generally composed of 
different individuals.  Other than when one serves as a sub adviser to 
the other, their investment decisions are made independently, and their 
clients are generally different organizations.

	FMR Corp. and FIL are of the view that they are not acting as a 
"group" for purposes of Section 13(d) under the Securities Exchange Act 
of 1934 (the "1934" Act) and that they are not otherwise required to 
attribute to each other the "beneficial ownership" of securities 
"beneficially owned" by the other corporation within the meaning of 
Rule 13d-3 promulgated under the 1934 Act.  Therefore, they are of the 
view that the shares held by the other corporation need not be 
aggregated for purposes of Section 13(d). However, FMR Corp. is making 
this filing on a voluntary basis as if all of the shares are 
beneficially owned by FMR Corp. and FIL on a joint basis.

	FIL may continue to have the International Funds or other 
accounts purchase shares subject to a number of factors, including, 
among others, the availability of shares for sale at what FIL considers 
to be reasonable prices and other investment opportunities that may be 
available to the International Funds.

	FIL intends to review continuously the equity position of the 
International Funds and other accounts in the Company.  Depending upon 
its future evaluations of the business and prospects of the Company and 
upon other developments, including, but not limited to, general 
economic and business conditions and money market and stock market 
conditions, FIL may determine to cease making additional purchases of 
shares or to increase or decrease the equity interest in the Company by 
acquiring additional shares, or by disposing of all or a portion of the 
shares.

	FIL does not have a present plan or proposal which relates to or 
would result in (i) an extraordinary corporate transaction, such as a 
merger, reorganization, liquidation, or sale or transfer of a material 
amount of assets involving the Company or any of its subsidiaries, (ii) 
any change in the Company's present Board of Directors or management, 
(iii) any material changes in the Company's present capitalization or 
dividend policy or any other material change in the Company's business 
or corporate structure, (iv) any change in the Company's charter or by-
laws, or (v) the Company's common stock becoming eligible for 
termination of its registration pursuant to Section 12(g)(4) of the 
1934 Act.

	FIL  has sole power to vote and the sole power to dispose of  
125,400  shares. FIL, FMR Corp., through its control of Fidelity, and 
FASST each has sole power to vote and to dispose of 76,000 shares held 
by FASST.



SCHEDULE 13G - TO BE INCLUDED IN STATEMENTS
FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)
RULE 13d-1(f)(1)  AGREEMENT

	The undersigned persons, on February 01, 1999, agree and consent 
to the joint filing on their behalf of this Schedule 13G in connection 
with their beneficial ownership of the common stock of KLA-Tencor 
Corporation at December 31, 1998.

FMR Corp.

By   /s/Eric D. Roiter   			
	Eric D. Roiter
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of FMR Corp. and its direct and indirect 
	subsidiaries

Edward C. Johnson 3d

By   /s/Eric D. Roiter   			
	Eric D. Roiter
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of Edward C. Johnson 3d

Abigail P. Johnson

By   /s/Eric D. Roiter   			
	Eric D. Roiter
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of Abigail P. Johnson

Fidelity Management & Research Company

By   /s/Eric D. Roiter   			
	Eric D. Roiter
	V.P. and General Counsel