Electric field‐induced second‐harmonic generation (EFISHG) is shown to be a very powerful method for contactless sampling of high‐speed electrical signals on silicon millimeter‐wave devices. We present picosecond resolution EFISHG measurements of 2 GHz sinusoidal signals on a photoconductive silicon‐on‐sapphire antenna. We further demonstrate the application of the EFISHG technique for spatial mapping of free‐running microwave signals in silicon. ©1996 American Institute of Physics.