Exhibit 99.1

CERTIFICATION OF CHIEF EXECUTIVE OFFICER AND CHIEF FINANCIAL OFFICER

PURSUANT TO

18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

I, Yagyensh C. Pati, certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that the Quarterly Report of Numerical Technologies, Inc. on Form 10-Q for the quarterly period ended June 30, 2002 fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 and that information contained in such 10-Q fairly presents in all material respects the financial condition and results of operations of Numerical Technologies, Inc.

Dated August 8, 2002	By:	/s/    YAGYENSH C. PATI
	Name:	Yagyensh C. Pati
	Title:	Chief Executive Officer during the quarter ended June 30, 2002 and through July 31, 2002

I, Richard S. Mora certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that the Quarterly Report of Numerical Technologies, Inc. on Form 10-Q for the quarterly period ended June 30, 2002 fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 and that information contained in such 10-Q fairly presents in all material respects the financial condition and results of operations of Numerical Technologies, Inc.

Dated August 8, 2002	By:	/s/    RICHARD S. MORA
	Name:	Richard S. Mora
	Title:	Chief Financial Officer