Thin films of polyaniline (PANI) titanium dioxide (TiO2) nanocomposites prepared with and without surfactant (tetradecyltrimethylammonium bromide, TTAB) were formed by spin coating onto chemically cleaned p-type silicon substrates. The current-voltage characteristics of the Au/PANI TiO (2)/p-Si/Al and Au/PANI TiO (2) TTAB/p-Si/Al heterojunctions had rectifying behavior with the potential barrier formed between the polymeric thin films and p-Si semiconductor, and they were analyzed on the basis of the standard thermionic emission (TE) theory. Cheung functions combined with conventional forward I-V characteristics were used to obtain diode parameters such as barrier height, ideality factor and series resistance (R (s) ). The values of barrier height, ideality factor and R (s) were found as 0.496 +/- 0.003 eV, 2.313 +/- 0.067 and 23.633 +/- 7.554 Omega for the Au/PANI TiO (2)/p-Si/Al device; 0.494 +/- 0.003 eV, 2.167 +/- 0.018 and 12.929 +/- 2.217 Omega for the Au/PANI TiO (2) TTAB/p-Si/Al device. In addition, the energy distributions of the interface state density of the devices were determined from the forward I-V characteristics by taking into account the bias dependence of the ideality factor and barrier height. It was seen that the PANI TiO (2) TTAB/p-Si device had slightly higher interface state density values than those of the PANI TiO (2)/p-Si device.