A p-type InP buffer layer containing Zn in a low concentration and an undoped InP buffer layer having a carrier concentration of 3.times.10.sup.17 cm.sup.-3 or less are stacked on a p-type InP substrate containing Zn. On the undoped InP buffer layer, a Mg-doped p-type InP cladding layer, an InGaAsP optical confinement layer, an InGaAsP MQW active layer, an n-type InGaAsP optical confinement layer, and an n-type InP cladding layer are successively stacked. The diffusion of Zn from the p-type InP substrate into the InGaAsP MQW active layer is suppressed. Moreover, a steep doping profile can be formed in the vicinity of the active layer so that deterioration of device characteristics is suppressed.