Semiconductor Substrate and Semiconductor Device Including the Same

A semiconductor substrate and a semiconductor device are provided. The semiconductor substrate includes a base substrate, a first silicon germanium layer on the base substrate and a second silicon germanium layer on the first silicon germanium layer. A germanium fraction of the second silicon germanium layer decreases in the direction away from the base substrate, and a germanium fraction of a lowermost part of the second silicon germanium layer is greater than a germanium fraction of an uppermost part of the first silicon germanium layer.