We grew Si1−x, Gex / Si / Si1−xGex heterostructures with abrupt interfaces for a high-speed device application. In order to eliminate the interface and the impurity scatterings, a two-stepsolid-phase epitaxy (SPE) was developed newly. This SPE can obtain an abrupt interface between the upper Si1−xGex. and the Si-channel layers as well as a sharp Sb-doping profile in the upper Si1−xGex layer. Single-step SPE growth of the Si1−xGex. layer including the Sb-doped layer caused solid state diffusion of Sb and made the doping-profile difficult to control. A two-step SPE, (that is, two independent SPE processes forming the Si1−xGex. and the Sb-doped layers), obtained a sharp Sb depth profile and high electrical activation in the Sb-doped Si1−xGex. layer. However, the number of modulation-doped carriers in the Si channel layer was small. Calculation of the carrier distribution between the channel and the doped layer suggests that the carrier density in the channel is low when the Sb-doping profile is extremely sharp; thus, precise control of the modulation-doped-carrier density by optimizing the thickness of the Sb-doped layer is crucial for operating modulation-doped field-effect transistors (MODFETs).