A semiconductor device for converting incident light into an electric current includes a semiconductor substrate; an electrode embedded in the semiconductor substrate; an insulation film contacting the electrode in the semiconductor substrate; a first semiconductor region of a first conductivity type, a second semiconductor region of a second conductivity type and a third semiconductor region of the first conductivity type, formed sequentially in a depth direction from a side of a front face of the semiconductor substrate; and a fourth semiconductor region of the second conductivity type contacting the insulation film and the second semiconductor region. An impurity concentration of the fourth semiconductor region is greater than an impurity concentration of the second semiconductor region.