A simple method for measuring interface state density distribution of an MIS capacitor is proposed. The method is the expanded one which is based on comparing a measured quasistaticC‐Vcurve to ideal characteristics. The measurement can be achieved semiautomatically and simultaneously with the quasistatic capacitance measurement by using analog systems. And rather time‐consuming computer calculation is not necessary. The completed apparatus can measure the interface state density in the range of 1010−3×1012/cm2· eV for standard Al&sngbnd;SiO2&sngbnd;Si capacitors. It is necessary for precise measurement to determine accurately the doping density of substrate and insulator capacitance.