EXHIBIT 23(a) CONSENT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS We consent to the incorporation by reference in the Registration Statement (Form S-8) pertaining to the Jacobs Engineering Group Inc. 1999 Stock Incentive Plan of our report dated November 3, 1999, with respect to the consolidated financial statements of Jacobs Engineering Group Inc. included in its Annual Report (Form 10-K) for the year ended September 30, 1999, filed with the Securities and Exchange Commission. Ernst & Young LLP June 8, 2000