A field-effect transistor (FET) with thin films of picene has been fabricated on SiO(2) gate dielectric. The FET showed p-channel enhancement-type FET characteristics with the field-effect mobility, mu, of 1.1 cm(2) V(-1) s(-1) and the on-off ratio of >10(5). This excellent device performance was realized under atmospheric conditions. The p increased with an increase in temperature, and the FET performance was improved by exposure to air or O(2) for a long time. This result implies that this device is an air (O(2))-assisted FET. The FET characteristics are discussed on the basis of structural topography and the energy diagram of picene thin films.