Al/Maleic Anhydride (MA)/p-Si metal-polymer-semiconductor (MPS) structures were prepared on p-Si substrate by spin coating and these MPS structures had a good rectifying behavior. The capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics of Al/MA/p-Si structures were investigated in the frequency (f) range of 1kHz-10MHz at room temperature. The parameters of diodes such as ideality factor, series resistance, barrier height and flat band barrier height were calculated from the forward bias I-V characteristics. The investigation of interface states density and series resistance from capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics in the MPS structures with thin interfacial insulator layer have been reported in order to explain the electrical characteristics of metal/polymer/semiconductor (MPS) with Maleic anhydride (MA) interface. The values of interface states density D-it and series resistance R-s were calculated from measurements of C and G. The values of interface states density D-it and series resistance R-s were calculated from measurements of C and G. These values of D-it and R-s were responsible for the non-ideal behavior of I-V and C-V characteristics. TheI-V, C-V-f and G-V-f characteristics confirm that the barrier height, D-it and R-s of the diode are shown parameters that strongly dependent on the electrical parameters in the MPS structures.