The disclosed subject matter includes a semiconductor optical device with a stable optical characteristic, an excellent radiant efficiency, and a high mounting reliability. A casing can be configured with a concaved-shaped cavity that includes an opening and a bottom portion. Each of one end portions of first/second lead frame electrodes 3a, 3b can be exposed on the bottom portion. The first one end portion can include an optical chip mounted thereon, and the second one end portion can be connected to another electrode of the optical chip via a bonding wire. The first lead frame electrode extends from an outside surface substantially perpendicular to the bottom portion and is bent in a direction towards the opening. The second lead frame electrode extends from an outside surface of the casing that is opposite to the outside surface from which the first electrode extends. Various physical configurations of the electrodes are disclosed.