To provide a semiconductor device having a compact electrostatic discharge protection transistor.

The semiconductor device has an insulating gate field-effect transistor 17 including: a gate electrode 14 formed on a semiconductor layer 12 of a first conductivity type via a gate insulating film 13; a first impurity diffusion layer 15 of a second conductivity type, formed along a gate width direction Y of the gate insulating electrode 14; and a second impurity diffusion layer 16 of a second conductivity type, having a body portion 16a disposed opposite the first impurity diffusion layer 15 along the gate width direction Y and a plurality of projections 16b projecting from the body portion 16b to the opposite side from the gate electrode 14, the width Wd1 of the gate electrode 14 in a gate width direction X being larger than the width Ws1 of the first impurity diffusion layer 15 in the gate length direction X.