A field-effect transistor includes: a substrate; a source electrode; a drain electrode; a gate electrode; a semiconductor layer in contact with the source electrode and with the drain electrode; and a gate insulating layer insulating between the semiconductor layer and the gate electrode. The gate insulating layer comprising at least a polysiloxane having a structural unit represented by a general formula (1): in the general formula (1), R1 represents a hydrogen atom, an alkyl group, a cycloalkyl group, a heterocyclic group, an aryl group, a heteroaryl group, or an alkenyl group; R2 represents a hydrogen atom, an alkyl group, a cycloalkyl group, or a silyl group; m represents 0 or 1; A1 represents an organic group including at least two groups selected from a carboxy group, a sulfo group, a thiol group, a phenolic hydroxy group, or a derivative of these groups.