PURPOSE: To obtain a semiconductor laser having a stable lateral mode, small astigmatism aberration and a longitudinally multiple mode difficult to be affected by the external return of light by providing optically discontinuous sections in part of the active layer of a refractive index wave guiding type semiconductor laser.

CONSTITUTION: Optically discontinuous sections are provided in part of an active layer 3 of a semiconductor laser having a refractive index wave guiding type resonator structure. For instance, a groove 12 is formed in an N-GaAs substrate 10, and if an M-Al0.4Ga0.6As clad layer 4 and an Al0.1Ga0.9As active layer 3 are formed thereon by means of the molecular beam epitaxial method or the like, sharp bends B1, B2 are made in the active layer 3 depending on the groove 12. Then, after the width of the active layer 3 is made to have a predetermined value by etching, a P-Al0.4Ga0.6 As clad layer 2 and a P-GaAs light absorbing layer 9 are grown by the liquid phase epitaxy. with this, the wave-guided light once runs out from the active layer to other layers at the optical discontinuous sections and is wave-guided again to the active layer through the other layers, so part of that light is absorbed in the other layers to increase the internal loss, thereby accomplishing the longitudinally multiple mode.