A surface emitting semiconductor laser which can perform laser oscillation in a single peak beam like that in a single lateral mode and a manufacturing method which can easily manufacture such a laser at a high yield are provided. When a surface emitting semiconductor laser having a post type mesa structure is formed on an n-type semiconductor substrate, a mesa portion is formed and up to a p-side electrode and an n-side electrode are formed. Thereafter, a voltage is applied across the p-side and n-side electrodes and the laser is subjected to a steam atmosphere while extracting output light, thereby forming an Al oxide layer onto a p-type Al.sub.wGa.sub.1-wAs layer as a top layer of a p-type DBR layer and forming refractive index distribution like that of a concave lens.