The characterization of microwave and millimeter-wave monolithic integrated circuits (MIMICs) using picosecond pulse-sampling techniques is developed with emphasis on improving broadband coverage and measurement accuracy. GaAs photoconductive switches are used for signal generation and sampling operations. The measured time-domain response allows the spectral transfer function of the MIMIC to be obtained. This measurement technique is verified by characterization of the frequency response (magnitude and phase) of a reference 50- Omega microstrip line and a two-stage K/sub a/-band MIMIC amplifier. The measured broadband results agree with those obtained from conventional frequency-domain measurements using a network analyzer. The application of this optical technique to on-wafer MIMIC characterization is described. >