It is an object to provide a semiconductor device comprising a short circuit protecting system capable of enhancing the detection precision of a collector current, thereby carrying out a reliable short circuit protection. An IGBT (1) having a collector (C) connected to a terminal (T1) and an emitter (E) connected to a terminal (T2) is provided, and has a sense emitter (SE) connected to a terminal (T2) through a variable resistor (VR1) to be a current and voltage converting section. A sense potential is output from an end on the sense emitter (SE) side of the variable resistor (VR1) and is given to a terminal (T11) of a current ratio detecting section (15). A gate of the IGBT (1) is connected to a terminal (T3) and an output of the current ratio detecting section (15) is connected to a terminal (T4).