Non-photolithographic organic thin film transistors (OTFTs) were fabricated using pentacene and SiNx films on p-Si (1 0 0) at room temperature to investigate both the effects of their device structure (two different types of OTFTs, top-electrode and bottom-electrode) and the pentacene film deposition-rate on their current-voltage characteristics. OTFTs of the top-electrode type were prepared by thermal evaporation at various deposition rates of 1, 3, 5 and 7 Angstrom/s. The top-electrode OTFTs exhibited 40 times higher amount of currents than the bottom-electrode OTFTs at the same bias conditions. An optimum OTFT was obtained using 5 Angstrom/s and exhibited the saturation current, I-D of approximately 4 muA at a gate bias of -40 V along with the field effect mobility of similar to0.046 cm(2)/V s and the on/off current ratio of similar to 10(5).