A field-effect transistor including: a substrate; a passivation layer; a gate insulating layer, formed between the substrate and passivation layer; a source electrode and a drain electrode, formed to be in contact with the gate insulating layer; a semiconductor layer, formed at least between the source electrode and drain electrode and being in contact with the gate insulating layer, source electrode, and drain electrode; and a gate electrode, in contact with the gate insulating layer and facing the semiconductor layer via the gate insulating layer, wherein the passivation layer is formed of a single layer containing a paraelectric amorphous oxide containing a Group A element, an alkaline earth metal and a Group B element, at least one selected from Ga, Sc, Y, and lanthanoid, and the gate insulating layer contains at least one selected from oxides of Si, nitrides of Si, and oxynitrides of Si.