A semiconductor laser, in which active layers are provided on the top surface of the mesa and the remainder surface in a substrate as a first semiconductor layer. Second semiconductor layers are provided on the active layers to such a thickness that the second semiconductor layer may not reach the first semiconductor layer on the mesa. Third semiconductor layers are provided on the second semiconductor layer to such a thickness that the third semiconductor layers may be flush with or higher than the first semiconductor layer on the mesa, so that the first semiconductor layer on the top surface of the mesa is just jointed with the third semiconductor layer on the remainder surface in the substrate.