PURPOSE: To improve the accuracy of temperature detection and to enable execution of such a quick and appropriate operation for a detected temperature as to lower a current so as to prevent thermal runaway, by forming a temperature detecting part in an active region of a semiconductor element.

CONSTITUTION: Cell parts making switching actions for continuity and interruption of a main current of a semiconductor element are provided. Besides, P-base regions 4 are formed selectively in the surface layer of an n-base layer 3 laminated on a p+ substrate 1 with an n+ buffer layer 2 interlaid. Particularly, a temperature detecting part is formed in an active region of the semiconductor element, that is, in a region between the cell parts. A diode 12 for temperature detection is provided as the temperature detecting part. Concretely, a P-region 10 is formed selectively in the surface layer of the n-base layer 3, an oxide film 11 is deposited on the surface of this region and further polysilicon is deposited thereon. According to this constitution, the accuracy of the temperature detection at the time of an operation of the semiconductor device is improved, execution of a quick and appropriate operation for a detected temperature is enabled and thereby thermal runaway can be prevented.