A semiconductor device includes source fingers and drain fingers provided on an active region of a nitride semiconductor layer alternately, gate fingers having a side edge and a distal edge, a first insulation film provided on the nitride semiconductor layer and covers a top face, the side and distal edges of the gate fingers, field plates provided on the first insulation film between the gate fingers and the drain fingers, a minimum distance between the side face of the first insulation film located on the side edge of the gate fingers and the field plate being at least 100 nm, and field plate interconnections provided on the first insulation film and located outside of the active region and electrically connected with the source fingers and the field plates, a minimum distance between the side face of the first insulation film located on the distal edge of the gate fingers and the field plate interconnections being at least 100 nm.