Field effect and capacitance-voltage characteristics of vacuum evaporated C-60 films are studied using metal-oxide-semiconductor structures such as metal/C-60/SiO2/n(+)-Si or or C-60/source-drain electrodes/SiO2/n(+)-Si. The electrical conductivity, carrier type, carrier concentration, and carrier mobility are estimated from these measurements. In particular, electrical characteristics during the deposition in vacuum and the influence of oxygen and nitrogen gases are investigated by the in-situ field effect measurement.