From 101: Take the Embarcadero Rd. exit all the way to El Camino.
Go across El Camino (Embarcadero becomes Galvez). Take a right on Arboretum, a left on Quarry, and a right on Welch.
900 Welch Road will be on the right.

From 280: Take the Sand Hill Rd. exit.
Continue on Sand Hill until you come to Pasteur Drive.
Take a right on Pasteur and a left on Welch.
900 Welch Road will then be on the left.