According to the present invention, a p-type ZnSe or p-type ZnSSe buffer layer is formed on a p-type GaAs substrate through at least single layer made of AlGaInP-based material and a II/VI-compound laser structure is formed on the p-type ZnSe or p-type ZnSSe buffer layer. Further, an AlGaAs-based buffer layer is provided between the substrate and the AlGaInP-based buffer layer. Further, the AlGaAs-based buffer layer has a composition expressed as Al.sub.0.5 Ga.sub.0.4 As and the AlGaInP-based buffer layer has a composition expressed as Al.sub.0.5 In.sub.0.5 P. Furthermore, a composition ratio x of Al in a buffer layer expressed as Al.sub.x Ga.sub.1-x As is modulated from 0 to 0.6 and a composition ratio y of Al in a buffer layer expressed as (Al.sub.y Ga.sub.1-y).sub.0.5 In.sub.0.5 P is modulated from 0 to 1. According to the present invention, an operation voltage of the II/VI-compound semiconductor laser can be reduced and the green or blue color semiconductor laser of low operation voltage can be obtained. This semiconductor laser can continuously be operated at room temperature and also operated with a long life span.