The junction temperature of a field effect transistor is detected with a higher degree of accuracy than in the past. A semiconductor device controls multiple field effect transistors that configure a power conversion device, and includes a differential amplifier and a controller that controls ON/OFF of the multiple field effect transistors. The differential amplifier detects the potential difference between a source and a drain of a field effect transistor that is controlled in the OFF state by the controller and that induces an electric current flowing through the body diode thereof, among the multiple field effect transistors.