A semiconductor device includes a first insulating film, a first optical waveguide and a second optical waveguide. The first insulating film has a first surface and a second surface opposite to the first surface. The first optical waveguide is formed on the first surface of the first insulating film. The second optical waveguide is formed on the second surface of the first insulating film. The second optical waveguide, in plan view, overlaps with an end portion of the first optical waveguide without overlapping with another end portion of the first optical waveguide.