A high-output semiconductor laser of a real index-guided structure comprises: a first conductive type clad layer; active layer for emitting light by current injection; second conductive type first clad layer; second conductive type second clad layer as a ridge waveguide; current-blocking layer formed in both sides of the second conductive type second clad layer and having a larger band gap than those of the second conductive type first and second clad layers; and second conductive type third clad layer having a mobility enough to guide a current to the second conductive type second clad layer and prevent a flow of a leak current into the current-blocking layer.