The present invention prevents breakage of a gate insulating film of a MOS device and provides a nitride semiconductor device having improved reliability. An SBD metal electrode provided between a drain electrode and a gate electrode is configured to form a Schottky junction with an AlGaN layer. Further, the SBD metal electrode and a source electrode are connected and electrically short-circuited. Consequently, when an off signal is inputted to the gate electrode, a MOSFET part is turned off and the drain-side voltage of the MOSFET part becomes close to the drain electrode voltage. When the drain electrode voltage increases, the SBD metal electrode voltage becomes lower than the drain-side voltage of the MOSFET part, thus the drain side of the MOSFET part and the drain electrode are electrically disconnected by the SBD metal electrode.