Amorphous-silicon thin-film transistors (a-Si TFTs) have been fabricated by using an a-Si layer deposited by low-temperature thermal-CVD method using higher silanes. The TFT with thermally grown SiO2 gate was operated in both the n-channel mode and the p-channel mode. The maximum field-effect mobility and typical on/off current ratio were 1.5 cm2/Vs and 107 for the n-channel operation, and 0.2 cm2/Vs and 106 for the p-channel operation, respectively. Free electron mobility in the conduction band and free hole mobility in the valence band have been estimated, using the temperature dependence of the field-effect mobilities. It was found that the hole mobility is as high as the electron mobility.