An optical semiconductor device includes an optical semiconductor chip, a light permeable member covering the chip, and a reflector formed with an accommodation space for accommodating the light permeable member. The light permeable member includes a convex lens for converging light emitted from the optical semiconductor chip. The reflector includes a reflecting surface for reflecting light emitted from the optical semiconductor chip. At least part of the convex lens is located within the accommodation space of the reflector. The light permeable member includes an extension engaging and extending along the reflecting surface. The extension includes a light emitting surface surrounding the convex lens.