A V-channeled substrate inner strip (VSIS) semiconductor laser includes a p-Ga.sub.1-31 y Al.sub.y As active layer sandwiched between a P-Ga.sub.1-x Al.sub.x As first cladding layer and an n-Ga.sub.1-x Al.sub.x As second cladding layer. The AlAs mole fraction x of the first and second cladding layers is selected between about 0.45 and 0.52 in order to minimize the mode competition noise at an operating temperature. In a preferred form, the cavity length is longer than 300 .mu.m so as to minimize the occurrence of the mode competition noise at the operating temperature. Furthermore, the reflectivity R.sub.1 of the front facet and the reflectivity R.sub.2 of the rear facet are selected to satisfy the condition 0.1.ltoreq.ln(1/R.sub.1 .multidot.R.sub.2).ltoreq.1.