A semiconductor laser comprising a substrate having a two step-striped channel; and a double heterostructure-laser-operating area having successively a cladding layer, an active layer and a second cladding layer on the substrate. The two step-striped channels are composed of a first channel and a second channel having a width which is narrower than the width of the first channel and having a depth which is deeper than the depth of the first channel. The second channel is positioned in the center portion of the first channel, thereby allowing current injected into the active layer to flow into the center portion of the two step-striped channel.