PURPOSE: To acquire a flat Ge epitaxial layer by forming a first Ge growth layer on a Ge substrate by using germane gas and by forming a second Ge growth layer thereon without exposing it to air at specified different growth temperatures, respectively.

CONSTITUTION: After a surface of a Ge substrate is etched, cleaned by wash and dried, it is contained in a growth chamber 1 of a vapor epitaxial device and oxide on the surface is removed. Then, Ge epitaxial growth is carried out at a temperature of 400°C or lower by using GeH4 gas. Thereafter, GeH4(is supplied at a growth temperature of 400°C or higher without exposing the Ge growth layer surface in air and a second Ge growth layer is formed on the first Ge growth layer. Thereby, a flat and thick Ge layer can be formed.