An approach for the controlled formation of thin strained silicon layers based on strain transfer in an epitaxial Si/ SiGe/ Si͑100͒ heterostructure during the relaxation of the SiGe layer is established. He + ion implantation and annealing is employed to initiate the relaxation process. The strain transfer between the two epilayers is explained as an inverse strain relaxation which we modeled in terms of the propagation of the dislocations through the layers. Effcient strain buildup in the Si top layer strongly depends on the Si top layer thickness and on the relaxation degree of the SiGe buffer. This letter presents a process for strain transfer within an epitaxial Si/ SiGe/ Si͑100͒ heterosystem and the involved theoretical rationale. As strained silicon ͑sSi͒ permits a significant improvement of nanoelectronic devices, due to a large enhancement of the mobility of the electrons and holes, this material presently receives enormous interest. 1 Our approach permits the formation of a sSi layer by epitaxial growth of a thin ϳ200 nm heterosystem, unlike the most common approach, which involves the growth of a thick (several m) relaxed SiGe buffer layer, and the polishing and overgrowth of the strained layer. 2 Here, a cubic Si/strained SiGe/ Si͑100͒ heterostructure is formed first. Then the elastic energy stored in the pseudomorphic Si 1−x Ge x layer is relaxed in a controlled way to transform the cubic top layer into sSi. In order to initiate this inverse strain relaxation process a He + implantation into the Si͑100͒ substrate and an annealing step are conducted. During this process a narrow defect band underneath the SiGe/ Si substrate interface is generated. It provides a high density of dislocation loops as sources for misfit dislocations (MDs) yielding efficient strain relaxation during annealing with low densities of threading dislocations (TDs). 3,4 For the strain transfer we make use of the propagation of the dislocations from the bottom of the relaxing SiGe layer towards the surface into the Si cap. This process differs from purely thermally induced strain relaxation where low densities of dislocations are nucleated randomly at the surface. We model the strain buildup in the Si layer by considering the forces acting on the dislocations and their resulting motion through the layers in detail. Our approach also differs from strain transfer between a film and a compliant substrate where only limited areas can be transformed and the misfit strain is diluted due to the elastic energy balance the two layers. 5