The GaAs‐GaAlAs graded‐index separate confinement heterostructure was grown selectively by molecular beam epitaxy on a SiO2‐masked GaAs (100) substrate. The stripe windows on the SiO2mask were 10 &mgr;m in width and were oriented along [011¯] direction. The laser diodes thus fabricated lased in a single longitudinal mode with a side mode suppression ratio of 95:1. Both the longitudinal mode and the single‐lobe far‐field pattern were stable up to 4Ith.