A semiconductor device which achieves reductions in malfunctions and operating characteristic variations by reducing the gain of a parasitic bipolar transistor, and a method of manufacturing the same are provided. A silicon oxide film (6) is formed partially on the upper surface of a silicon layer (3). A gate electrode (7) of polysilicon is formed partially on the silicon oxide film (6). A portion of the silicon oxide film (6) underlying the gate electrode (7) functions as a gate insulation film. A silicon nitride film (9) is formed on each side surface of the gate electrode (7), with a silicon oxide film (8) therebetween. The silicon oxide film (8) and the silicon nitride film (9) are formed on the silicon oxide film (6). The width (W1) of the silicon oxide film (8) in a direction of the gate length is greater than the thickness (T1) of the silicon oxide film (6).