The present invention relates to a nitride semiconductor laser device provided with a window layer on a light-emitting end face of the resonator which comprises an active layer of nitride semiconductor between the n-type nitride semiconductor layers and the p-type nitride semiconductor layers, in which at least the radiation-emitting end face of said resonator is covered by said window layer comprising monocrystalline nitride of general formula Al.sub.xGa.sub.1-x-yIN.sub.yN, where 0.ltoreq.x+y.ltoreq.1, 0.ltoreq.x.ltoreq.1 and 0.ltoreq.y<1, having a wider energy gap than that of the active layer and being formed at a low temperature so as not to damage said active layer. Formation of such a window layer improves significantly the performance of the nitride laser device according to the invention.