Al/P2ClAn/p-Si/Al structure was obtained by the evaporation of the polymer P2ClAn on the front surface of p-type silicon substrate. The P2ClAn emeraldine salt was chemically synthesized by using propionic (C2H5COOH) acid. The current-voltage (I-V) characteristic of the structure was measured at room temperature. The capacitance-voltage-frequency (C-V-f) in terms of interface states over the frequency range of 10 kHz to 3 MHz has been investigated. The capacitance has decreased with increasing frequency, due to the interface states distribution. From the forward bias I-V plot for the sample, the ideality factor (n) and zero-bias barrier height (Phi(bp,0)) were obtained as 4.84 and 0.787 eV, respectively. Under forward bias, the high value of the ideality factor and the dispersion in capacitance could be due to the interface state distribution, the interfacial insulator layer, the conducting polymer on the interface and inhomogeneity of the barrier height. The energy distributions and the relaxation times of the interface states were determined in the energy range of (0.387 - E-v) to (0.787 - E-v) eV. (C) 2009 Elsevier B.V. All rights reserved.