To surely prevent the overheat of a main element by accurately detecting the temperature of the main element constituting a semiconductor device that controls an AC load.

The semiconductor device is configured such that: an overheat detection part composed of an element having a positive temperature characteristic is arranged at a gate of the main element that constitutes the semiconductor device; the temperature of the main element is directly detected by the overheat detection part; and a gate signal is blocked so that the temperature of the main element does not reach the junction temperature of the element. By this configuration, the main element is prevented from being broken by the overheat without the need for using a complicated circuit constitution.