Optical semiconductor device

An optical semiconductor device, comprising:

• an optical element mounted on a substrate;
• and
• a window lid configured to seal the optical element in a space on the substrate, the window lid including a frame member and a glass plate member, the frame member being formed by performing drawing on a metal plate,
• wherein:
• the frame member includes a top plate part having an opening window, a peripheral side plate part connected to a peripheral edge of the top plate part so as to surround a space on the top plate part, and a flange part extending outward from a peripheral edge of the peripheral side plate part on a side opposite from the top plate part, the flange part being fixed to the substrate;
• and
• the glass plate member is contained in the space formed by the top plate part and the peripheral side plate part of the frame member, the glass plate member being welded by matched welding to a surface of the top plate part on a side toward the substrate and an internal surface of the peripheral side plate part.