To provide a field-effect transistor, containing: a gate electrode configured to apply gate voltage; a source electrode and a drain electrode, both of which are configured to take out electric current; an active layer formed of a n-type oxide semiconductor, provided in contact with the source electrode and the drain electrode; and a gate insulating layer provided between the gate electrode and the active layer, wherein work function of the source electrode and drain electrode is 4.90 eV or greater, and wherein an electron carrier density of the n-type oxide semiconductor is 4.0×1017 cm−3 or greater.