SEMICONDUCTOR DEVICE

PURPOSE:To prevent overvoltage between a drain and a source, by making the gate of one cell of MOS cells, which are formed on the same substrate, independent, and connecting the gate to a voltage dividing point between voltage dividing resistors which are connected between the drain and the source. CONSTITUTION:A main transistor 7 for switching and a transistor 8 for protection from overvoltage are constituted by N-channel enhancement type MOS cells on the same substrate. A voltage dividing point N between voltage dividing resistors 10 and 11, which are connected between a drain 5 and a source 6, is connected to the gate 8a of the transistor 8. When overvoltage is applied across the drain and the source, the voltage between the gate 8a and the source 6 is increased. Then the transistor 8 becomes conductive, and the overvoltage is absorbed. A high-speed overvoltage which is higher than at the operating speed of the transistor 8 is bypassed through a capacitor 9 between the drains and the sources of the transistors 7 and 8. Even the overvoltage having relatively long pulse width can be absorbed by the transistor 8.