PURPOSE: To make an impurity concentration constant, by diffusing metal on the surface of a material to be processed which is housed in a reaction chamber, while supplying an organic metal gas and a gas for controlling steam pressure.

CONSTITUTION: A semiconductor laser element 1 has a multilayer growth film 3 on a substrate 2 comprising n-type GaAs and of a structure having an anode electrode 4 on the upper surface thereof and a cathode electrode 5 on the lower surface. The element is manufactured by vertically and horizontally dividing a plurality of the semiconductor laser element components formed vertically and horizontally and regularly on a thin and large wafer 13. When Zn is diffused partially on the wafer, the wafer 13 is set on a susceptor 16 in a ball jar 14 and a reaction chamber 15 is controlled at a desired vacuum degree. After a hydrogen gas is supplied into the reaction chamber 15 through a line 20 and purged, dimethylzinc 25 is supplied and then arsine 28 is supplied. As a result, the whole main surface of the wafer 13 is uniformly heated and uniform Zn diffusion can be performed.