The performances of a semiconductor device are improved. The semiconductor device includes an insulation layer, an optical waveguide part formed over the insulation layer, and including a p type semiconductor region and an n type semiconductor region formed therein, and an interlayer insulation film formed over the insulation layer in such a manner as to cover the optical waveguide part. At the first portion of the optical waveguide part, in a cross sectional view perpendicular to the direction of extension of the optical waveguide part, the n type semiconductor region is arranged at the central part of the optical waveguide part, and the p type semiconductor region is arranged in such a manner as to surround the entire circumference of the n type semiconductor region.