A semiconductor device includes a plurality of high-voltage insulated-gate field-effect transistors arranged in a matrix form on the main surface of a semiconductor substrate and each having a gate electrode, a gate electrode contact formed on the gate electrode, and a wiring layer which is formed on the gate electrode contacts adjacent in a gate-width direction to electrically connect the gate electrodes arranged in the gate-width direction. And the device includes shielding gates provided on portions of an element isolation region which lie between the transistors adjacent in the gate-width direction and gate-length direction and used to apply reference potential or potential of a polarity different from that of potential applied to the gate of the transistor to turn on the current path of the transistor to the element isolation region.