We report the application of optical second‐harmonic generation to the measurement of ultrafast electrical pulses. The technique relies on the sensitivity of the second‐harmonic response to electric fields in centrosymmetric materials. Electrical pulses propagating on a silicon‐based coplanar transmission line have been characterized with subpicosecond time resolution and 100 mV/&sqrt;Hz sensitivity. We have measured the bias dependence of the second harmonic intensity over a 20 V range and have used this data to calibrate the transient response. The observed full‐width at half maximum response time of the SHG waveform is ∼1 ps, which is consistent with the value obtained from an electronic cross‐correlation measurement. ©1996 American Institute of Physics.