The present invention relates to a semiconductor substrate, a semiconductor device with high carrier mobility and a method of manufacturing the same. According to the present invention, there are provided a semiconductor substrate comprising a silicon substrate, a single crystal germanium layer formed on the silicon substrate, and a silicon layer formed on the single crystal germanium layer; a semiconductor device comprising a gate electrode formed on the semiconductor substrate, and junctions formed in the substrate at both sides of the gate electrode; and a method of manufacturing the semiconductor device. Therefore, carrier mobility of channels can be enhanced since the channels of semiconductor devices are placed within the germanium layer. Further, since the silicon layer is formed on the germanium layer, the reliable gate insulation film can be formed and a leakage current produced in a junction layer can also be reduced. Moreover, the same effect can be obtained without using an expensive germanium wafer. Accordingly, since conventional processes and equipment can be used as they are, highly efficient semiconductor devices can be fabricated without increase of a unit cost of production.