Perylene–diimide (PDI) organic semiconductor was prepared on n-type Si wafer using spin coating method. The dielectric permittivity, conductivity and electric modulus properties of PDI structure were characterized by means of the capacitance–voltage and the conductance–voltage measurements at the voltage range from 0 V to 300 mV and the frequency range from 30 kHz to 1 MHz. It is observed that the dielectric dispersion is uniformly decreased with the frequency, and then approach nearly to a fixed value at higher frequencies. However, the imaginary (M″) part of electric modulus has a peak for all the applied voltage values and the peak shifts to the higher frequencies with decreasing voltage. The peak observed in the figure is attributed to the dielectric relaxation. Furthermore, it has been reported that the Cole–Cole curves has one relaxation.