Patent ID: 8891570

Claim:
An optical semiconductor device formed on an InP semiconductor substrate, comprising: a first clad layer of a first conductivity type and having an air ridge shape; a first conductivity type semiconductor layer disposed on a lower layer side which is the InP semiconductor substrate side of the first clad layer and including at least one layer having a composition different from a composition of the first clad layer; Al-based semiconductor multi-layer films disposed on the lower layer side of the first conductivity type semiconductor layer, the AL-based semiconductor mutli-layer films being formed by overlapping a plurality of semiconductor layers including an Al element, and having a quantum well active layer; a second clad layer disposed on the lower layer side of the Al-based semiconductor multi-layer films and is of a second conductivity type; and at least one burial semiconductor layer in contact with two opposite common side walls formed by the first conductivity type semiconductor layer and the Al-based semiconductor multi-layer films, wherein an end surface of an upper layer side of the burial semiconductor layer has a surface which has substantially the same height as an end surface of an upper surface side of the first conductivity type semiconductor layer, and a lower layer side thereof extends so as to cover at least the Al-based semiconductor multi-layer films.