Abstract: The invention relates to a semiconductor diode laser whose strip-shaped active region is limited by an end face which is curved for forming a lens of a given strength. A disadvantage of the known diode is that it has a comparatively high starting current. This is found to be caused inter alia by the etching necessary for forming a curved end face. During etching, unevennesses arise in the curved end face where scattering of the generated radiation occurs. This increases the starting current of the diode. A diode according to the invention is characterized in that the curved end face is covered with a covering layer of a material having a refractive index different from that of the active layer, and the refractive index of the covering layer and the curvature of the end face are so chosen that the scattering of the generated radiation is a minimum for the given strength of the lens.