Sn/ PANI/ p- Si/ Al heterojunctions were fabricated by electropolymerization of aniline on chemically cleaned p- Si substrates. Current - voltage characteristics of Sn/ PANI/ p- Si/ Al heterojunctions measured in the temperature range 140 280 K are presented and analyzed. Although these devices were clearly rectifying, their I - V characteristics were non- ideal, which can be judged from the nonlinearity in the semi- logarithmic plots. The high values of the ideality factor n depending on the sample temperature may be ascribed to a decrease of the exponentially increasing rate in current due to space- charge injection into the PANI thin film at higher forward bias voltages. Careful analysis of the forward bias I - V characteristics on a log - log scale indicates that the space-charge-limited current ( SCLC) conduction controlled by an exponential trap distribution above the valence band edge dominates the current transport in the PANI/ p- Si diodes at high voltages. Furthermore, the PANI was characterized by using Fourier transform infrared ( FTIR) and ultraviolet - visible ( UV - vis) spectra.