Abstract: An improvement in conditions that protective functions of an insulated gate semiconductor device with a protection circuit incorporated therein are performed, an improvement in the cutoff of heating, the prevention of malfunctions and an improvement in ease of usage can be achieved.The insulated gate semiconductor device of the present invention comprises a power insulated gate semiconductor element (M9), at least one MOSFET (M1 through M7) for a protection circuit, for controlling the power insulated gate semiconductor element, a constant-voltage circuit using forward voltages developed across diodes (D2a through D2f) for the constant-voltage circuit, and voltage restricting diodes (D1 and D0a through D0d) for controlling the upper limit of a power supply voltage of the constant-voltage circuit. Power to be supplied to the voltage restricting diodes is supplied from an external gate terminal of the power insulated gate semiconductor element.

Abstract: Provided is a compounded power MOSFET which has a high positive and negative withstand voltages for the drain terminal relative to the source terminal, and can be formed on a single chip based on the conventional fabrication process of power MOSFETs. Power MOSFETs 10 and 11 have their drains connected together, the MOSFET 10 has its source and gate used for the source terminal 0 and gate terminal 1, respectively, of the compounded power MOSFET 60, and the MOSFET 11 has its source used for the drain terminal 2. The compounded power MOSFET includes a voltage comparator 50 which drives the MOSFET 11 to turn off when the terminal 2 has a negative voltage, and a voltage transmitter 51 which is connected between the terminal 1 and the gate of the MOSFET 11 to block a current flowing from the terminal 2 to the terminal 1 by way of the circuit 50 and transfer the voltage of the terminal 1 to the gate of the MOSFET 11.