A semiconductor device can reduce a leak current, and a manufacturing method can provide such a semiconductor device. A semiconductor device includes an isolating and insulating film formed on a main surface of a semiconductor substrate including a first conductivity type region, and also includes a field-effect transistor. The field-effect transistor includes a second conductivity type region neighboring to the isolating and insulating film, a gate electrode, a lower layer side wall film formed on a side surface of the gate electrode, an upper layer side wall film formed on the lower layer side wall film and containing a material different from that of the lower layer side wall film, and a high-melting-point metal silicide layer formed on the second conductivity type region. The upper surface of the isolating and insulating film is located at a level substantially equal to or lower than the main surface of the semiconductor substrate and higher than a junction boundary surface between the first and second conductivity type regions.