Abstract: Organic thin-film transistors based on the heavily doped silicon substrates were fabricated with two different designs: bottom and top contact configurations（referred to as BC-OTFTs and TC-OTFTs,respectively）.The influence of configurations on the device performance was investigated.The results indicate that good contact can be obtained with top contact;the mobility and the on/off ratio of TC-OTFTs are three orders of magnitude higher than those of BC-OTFTs.The thickness of gate insulator can also influence the device performance.At the same gate voltage,thinner gate insulator enhanced the field.As a result,more carriers can be accumulated to fill up more traps,so that the mobility and the operation current are enhanced subsequently.