A semiconductor device implementing a field plate is disclosed. The semiconductor device includes electrodes of a source, a gate, and a drain; an insulating film covering at least the drain electrode; a field plate that includes a first part overlapping with the gate electrode and a second part not overlapping with the gate electrode; and a source interconnect connected with the source electrode. A feature of the semiconductor device of the invention is that both of the first part and the second part are electrically connected with the source interconnection.