A semiconductor device which can effectively suppress a short channel effect and junction leakage is provided. A semiconductor device includes a field effect transistor. The field effect transistor includes a first semiconductor region of a first conductivity type, a gate electrode formed on a gate insulating film, and source and drain electrodes. The field effect transistor also includes second semiconductor regions of a second conductivity type. The field effect transistor further includes third semiconductor regions of the second conductivity type having an impurity concentration higher than that of the second semiconductor region and formed between the source electrode and the first and second semiconductor regions and between the drain electrode and the first and second semiconductor regions, and side wall insulating films formed on both the side surfaces of the gate electrode. The source electrode and the drain electrode are separated from the side wall insulating films.