A new metal‐semiconductor field‐effect‐transistor surface characterization technique is presented. The complex impedance (magnitude and phase) between the source and drain contacts is measured as a function of frequency and temperature. It is shown that the phase data exhibit peaks in the frequency spectrum that correspond to characteristic emission rates for surface‐state traps. Measurements at different temperatures provide the energetic position and capture cross section of dominant traps. The technique provides a relatively rapid surface characterization tool in comparison to deep‐level transient spectroscopy. ©1995 American Institute of Physics.