To provide a semiconductor device capable of preventing a switching element from being broken owing to yielding when an overvoltage is applied even when a temperature of a junction or channel of the switching element having a small margin of avalanche resistance rises.

A protective transistor 20 composed of a vertical MOSFET has a gate electrode 23 and a source electrode 22 formed on one surface of a semiconductor substrate 2 and has a drain electrode 21 formed on the other surface. A source electrode 12 present on one surface of a semiconductor substrate 1, in which an output transistor 10 is formed, and the one surface of the semiconductor substrate 2 are bonded with a conductive adhesive 6, and the source electrode 22 and gate electrode 23 are electrically connected to the source electrode 12 to be thermally and closely coupled. Drain electrode 11 and 21 are connected to each other by a lead wire 32. At a high temperature, the protective transistor 20 decreases in threshold to 0 V or below to be turned on, and takes partial charge of a part or the whole of an avalanche current of the output transistor.