The present invention provides a semiconductor laser device including a heat sink having one main surface, an n-AlGaAs cladding layer disposed on the main surface of the heat sink, an AlGaAs active layer disposed on the n-AlGaAs cladding layer and a p-AlGaAs cladding layer disposed on the AlGaAs active layer. An effective refractive index and a thermal resistance between a main surface on the heat sink side, of the AlGaAs active layer and a main surface on the heat sink side, of the n-AlGaAs cladding layer are respectively set smaller than those between a main surface on the side opposite to the heat sink, of the AlGaAs active layer and a main surface on the side opposite to the heat sink, of the p-AlGaAs cladding layer.