A simple four‐terminal conductance bridge circuit, which provides high‐resolution measurements of the current–voltage characteristics,dI/dVandd2I/dV2, as well as capacitance anddC/dVmeasurements, is presented. Current measurements in the wide range 1 nA–10 mA are possible and modulation voltages down to 1 &mgr;V can be used to achieve high resolution. The circuit has been used successfully for tunneling spectroscopy on GaAs–GaAlAs field effect transistor structures.