Abstract: A vapor-phase epitaxial process enabling easy growth of a III-V compound semiconductor layer including a .delta.-doped layer requires essentially no change or rearrangement of the conventional vapor-phase epitaxial reactor system but only a simple change in the method of controlling the system. The epitaxial process includes the step of feeding an epitaxial growth gas into a reactor vessel containing a III group element as a raw material and an epitaxial substrate made of a semiconductor to epitaxially grow a layer made of a III-V compound semiconductor on the substrate by the chloride CVD process.