Interface states in the metal‐oxide‐semiconductor (MOS) system have a great influence on the electrical properties of MOS capacitors and field‐effect transistors. Several methods for measuring the density of these interface states within the forbidden band gap of silicon employ differential capacitance versus gate bias (C‐V) measurement on MOS capacitors. We present here aC‐Vmeasurement technique utilizing the MOS transistor that extends the energy range of the high‐low frequency method to that of the low‐frequency technique.