A semiconductor laser element having a GaAs substrate formed thereon with an active layer of a strained quantum well construction provided with an In.sub.x Ga.sub.1-x As strained quantum well layer and a GaAs barrier layer and clad layers arranged up and down of said active layer through an epitaxial growth means. A lattice mismatching rate of the clad layer with respect to the substrate is less than 10.sup.-3.