A technique for a reverse conducting semiconductor device including an IGBT element domain and a diode element domain that utilize body regions having a mutual impurity concentration, that makes it possible to adjust an injection efficiency of holes or electrons to the diode element domain, is provided. When a return current flows in the reverse conducting semiconductor device that uses an NPNP-type IGBT, a second voltage that is higher than a voltage of an emitter electrode is applied to second trench gate electrodes of the diode element domain. N-type inversion layers are formed in the periphery of the second trench gate electrodes, and the electrons flow therethrough via a first body contact region and a drift region which are of the same n-type. The injection efficiency of the electrons to the return current is increased, and the injection efficiency of the holes is decreased. Due to this, an increase in a reverse recovery current can be prevented, and a switching loss caused in the diode element domain can be decreased.