A field-effect transistor including a semiconductor layer formed of an n-type metal oxide semiconductor, wherein the n-type metal oxide semiconductor includes indium oxide, wherein the indium oxide is n-type doped through introduction of one or more kinds of cations as dopants, and wherein the n-type metal oxide semiconductor has a peak detected at an angle corresponding to a (222) plane of indium oxide having a bixbite structure in an X-ray diffraction method using a two-dimensional detector.