Abstract: A distributed feedback semiconductor laser which achieves a phase shift for stabilizing the longitudinal mode without a substantial increase in reactive current and without introducing dimensional discontinuities in the laser stripe. The active layer of the laser is configured as a multi-quantum well and impurities are selectively diffused into the multi-quantum well to disorder a selected portion of the active layer. The disordered portion has an optical propagation constant which is different than that of the remaining stripe, and the difference in propagation constant coordinated with the length of the phase adjustment section produces a phase shift adequate to stabilize the laser longitudinal mode.