A method for fabricating a III-V Group compound semiconductor comprising a
step of epitaxially growing on an Al.sub.x Ga.sub.1-x As layer of lower Al
content an Al.sub.x Ga.sub.1-x As layer of higher Al content, in which
step a growth rate of the Al.sub.x Ga.sub.1-x As layer of higher Al
content is made slower than a growth rate of the Al.sub.x Ga.sub.1-x As
layer of lower Al content, thereby effectively inhibiting the occurrence
of starting points of abnormal growth at the interface between the two
layers.
