Optical semiconductor device

An optical semiconductor device, comprising:

• a substrate;
• a semiconductor multilayer which is formed on the substrate, and includes an optical functional layer;
• an insulating film formed on the semiconductor multilayer;
• and
• an electrode formed on a part of the insulating film,
• wherein the insulating film covers the semiconductor multilayer except for a region in which the semiconductor multilayer and the electrode are electrically connected to each other,
• wherein at least a part of a region of the insulating film that is over the semiconductor multilayer and overlapped with the electrode is thinner than a region of the insulating film that is over the semiconductor multilayer and not overlapped with the electrode, and
• wherein the at least the part of the region of the insulating film that is overlapped with the electrode is proximate to and located above the semiconductor multilayer.