A field-effect transistor including: a gate electrode, which is configured to apply gate voltage; a source electrode and a drain electrode, which are configured to take electric current out; an active layer, which is disposed to be adjacent to the source electrode and the drain electrode and is formed of an oxide semiconductor; and a gate insulating layer, which is disposed between the gate electrode and the active layer, wherein the gate insulating layer contains a paraelectric amorphous oxide containing a Group A element which is an alkaline earth metal and a Group B element which is at least one selected from the group consisting of Ga, Sc, Y, and lanthanoid, and wherein the active layer has a carrier density of 4.0×1017/cm3 or more.