SC 13G/A 1 SCHEDULE 13G/A SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G/A Under the Securities Exchange Act of 1934 LAM RESEARCH CORP. (Name of Issuer) COMMON STOCK (Title of Class of Securities) 512807108 (CUSIP Number) Check the following box if a fee is being paid with this statement. / / (A fee is not required only if the filing person: (1) has a previous statement on file reporting beneficial ownership of more than five percent of the class of securities described in Item 1; and (2) has filed no amendment subsequent there to reporting beneficial ownership of five percent or less of such class.) (See Rule 13d-7.) CUSIP No. 512807108 13G/A Page 1 of 3 Pages --------- --- --- 1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON J. & W. SELIGMAN & CO. INCORPORATED 13-3043476 2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) /x/ (b) /_/ 3) SEC USE ONLY 4) CITIZENSHIP OR PLACE OF ORGANIZATION DELAWARE NUMBER OF SHARES (5) SOLE VOTING POWER 1,355,500 BENEFICIALLY OWNED (6) SHARED VOTING POWER -0- BY EACH REPORTING (7) SOLE DISPOSITIVE POWER 1,355,500 PERSON WITH (8) SHARES DISPOSITIVE POWER -0- 9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 1,355,500 10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES 11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 4.94% 12) TYPE OF REPORTING PERSON IA CUSIP No. 512807108 13G/A Page 2 of 3 Pages --------- --- --- Item 1(a) Name of Issuer: LAM RESEARCH CORP. Item 1(b) Address of Issuer's Principal Executive Offices: 4650 CUSHING PARKWAY FREMONT, CA 94538 Item 2(a) Name of Person Filing: J. & W. SELIGMAN & CO. INCORPORATED Item 2(b) Address or Principal Business Office or, if none, Residence: 100 PARK AVENUE NEW YORK, NEW YORK 10017 Item 2(c) Citizenship: DELAWARE CORPORATION Item 2(d) Title of Class of Securities: COMMON STOCK Item 2(e) CUSIP Number: 512807108 Item 3 If this statement is filed pursuant to Rules 13-d, or 13-2(b), check whether the person is filing as a: Investment Adviser registered under Section 203 of the Investment Advisers Act of 1940 /X/ Item 4(a) Amount Beneficially Owned: 1,355,500 Item 4(b) Percent of Class: 4.94% Item 4(c) Number of shares as to which such person has: (i) sole power to vote or to direct the vote 1,355,500 (ii) shares power to vote or direct the vote -0- (iii) sole power to dispose or to direct the disposition of 1,355,500 (iv) shares power to dispose or to direct the disposition of -0- CUSIP No. 512807108 13G/A Page 3 of 3 Pages --------- --- --- Item 5 Ownership of Five Percent or Less of a Class: NOT APPLICABLE 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 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 statement is true, and correct. Lawrence P. Vogel Senior Vice President, Finance MAY 20, 1996 Date