PURPOSE: To provide an MOS semiconductor element with a built-in function of detecting overheat by connecting a resistor between a gate electrode and the first conductivity type region of a built-in diode and providing an overheat detecting signal terminal at the mid-point.

CONSTITUTION: Since a main current flowing from a source electrode 6 connected to a source terminal S in contact with an n region 3 to a drain electrode 7 connected to a drain terminal D in contact with the rear of an n substrate 1 can be turned on by applying voltage to a gate electrode 5, this MOS semiconductor element acts as an N-channel MOS switching element 10. A detector diode 20 composed of a p anode region 8 and an n cathode region 9 is integrated, while a resistance 30 composed of n region 12 is integrated on the surface layer of a p region. Therefore, the anode electrode 13 of the diode 20 is connected to the source terminal S, the cathode electrode 14 to a detecting signal terminal So, the electrode 15 of the resistance 30 to the detecting signal terminal So and an electrode 16 to a gate terminal G, thereby being able to protect the main element from overcurrent and the increase of an ambient temperature.