In this paper, we report the effect of optical power on interface state density (Dit) for the ultrasensitive single electron photodetector (photo-SET). To perform this work, Conductance–Capacitance–Voltage (C–G–V) techniques have been used, which form a method for the characterization of interface traps in MIS structures, taking into account the effect of the series resistance (Rs) at room temperature. To calculate the value of the density of interface states, (C–G–V) sweeps need to be corrected, analyzed and all extracted parameters would need to be recorded. Using Hill-Coleman method and a program developed using MATLAB, the calculated value of these interface state density (Dit) at 1 MHz was 2.4 · 1012 eV− 1 cm− 2.The value of the interface state density (Dit) increase with increasing optical power.