The present invention encompasses an organic field-effect transistor comprising an n-type organic semiconductor formed of a fullerene derivative having a fluorinated alkyl group which is expressed by the following chemical formula (wherein at least any one of R.sub.1, R.sub.2 and R.sub.3 is a perfluoro alkyl group or a partially-fluorinated semifluoro alkyl group each having a carbon number of 1 to 20), and a field-effect transistor production method comprising forming an organic semiconductor layer using the fullerene derivative by a solution process, and subjecting the organic semiconductor layer to a heat treatment in an atmosphere containing nitrogen or argon or in vacuum to provide enhanced characteristics to the organic semiconductor layer. The present invention makes it possible to form an organic semiconductor layer by a solution process and provide an organic field-effect transistor excellent in electron mobility and on-off ratio and capable of operating even in an ambient air atmosphere.