To provide a semiconductor device in which a rectifying element capable of reducing a leak current in reverse bias when a high voltage is applied and reducing a forward voltage drop Vf and a transistor element are integrally formed on a single substrate.A semiconductor device has a transistor element and a rectifying element on a single substrate. The transistor element has an active layer formed on the substrate and three electrodes (source electrode, drain electrode, and gate electrode) disposed on the active layer. The rectifying element has an anode electrode disposed on the active layer, a cathode electrode which is the drain electrode, and a first auxiliary electrode between the anode electrode and cathode electrode.