Abstract: A semiconductor device and a photonic semiconductor device are disclosed wherein, if it is assumed that “w” stands for the thickness of a metal electrode layer covering a contact layer and current-unfed regions, that “D” denotes the thickness of a plating layer formed on the metal electrode layer, that the boundary between the contact layer and any one of the current-unfed regions is taken as an origin, that a direction from the origin into the device interior is a positive direction, and that a direction from the origin toward any one of device facets is a negative direction, then a distance “d” between the origin and each facet of the plating layer is set to satisfy a relationship of d/w*[1−w/(w+D)]<20.