For the depletion and accumulation modes, equivalent circuits of MIS structure based on an organic P3HT thin film with an Al2O3 insulator are proposed. The frequency dependences of the capacitance and conductance of an organic MIS structure were simulated at a temperature of 300 K in the frequency range of 20 Hz – 2 MHz. It is shown that the measured values of the capacitance and conductance substantially depend on the thickness of the insulator layer, the thickness and specific conductance of the organic film, the parameters of surface traps, the frequency and bias voltage. Methods for determining the values of the basic elements of the equivalent circuit for the correct characterization of traps at the inorganic insulator – organic film interface are described.