A very important feature of present day semiconductor device technology is the measurement of the complex impedance or admittance characteristics of two‐terminal diodes or three‐terminal transistors. An electronic technique has been developed to automatically and continuously display the incremental conductance and capacitance of any two terminal nonlinear admittance as a function of applied dc bias over a frequency range 10 cps to 100 kc. The method employs phase sensitive detection to separate the in‐phase and quadrature components of the signal generated by a diode under test. Phase angle settings can be made to better than 0.1°. The system can measure over at least five orders of magnitude in admittance, and conductances as low as 0.001 &mgr;mho can be detected. The detection sensitivity of the apparatus is 0.0032 &mgr;V in a signal‐to‐noise ratio of 6.5×10−3. The performance of the system is described in terms of actual experimental data that have been obtained on various metal‐insulator‐semiconductor diodes.