Abstract: A semiconductor laser device containing a laser oscillation-operating area which comprises a Ga.sub.1-x Al.sub.x As (0.ltoreq.x.ltoreq.1) quantum well active layer, Ga.sub.1-y Al.sub.y As optical guiding layers interposing the quantum well active layer therebetween, and Ga.sub.1-z Al.sub.z As cladding layers superposed on the optical guiding layers, respectively, wherein the AlAs mole fraction y at the area of each of the optical guiding layers positioned in the vicinity of the interface of the optical guiding layers and the quantum well active layer meets the relationships y-z.gtoreq.0.3 and z-y.ltoreq.0.25.