PURPOSE: To improve reliability by forming side gates at the drain side of the gate electrode of a field-effect transistor and applying voltage different from that of the gate electrode to a side gate.

CONSTITUTION: A thin oxide film 4 is formed on a silicon substrate, a gate electrode 1, and the sidewalls of the gate and polysilicon is deposited on the whole surface and etched to form side gates 5 on the sidewalls of the gate electrode 1 as a main gate. Low-concentration impurity diffusion layers 6a and 6b are formed, resist 7 is patterned at a drain formation region, and the source-side side gate 5 is removed. Voltage different from that of the gate electrode 1 is applied to the side gate 5. Thereby a horizontal electric field near the drain is relaxed and generation of a hot carrier and decrease in the element characteristic of an MOA type field-effect transistor (MOSFET) are suppressed.