A strained silicon layer is grown on a layer of silicon germanium and a second layer of silicon germanium is grown on the layer of strained silicon in a single continuous in situ deposition process. Both layers of silicon germanium may be grown in situ with the strained silicon. This construction effectively provides dual substrates at both sides of the strained silicon layer to support the tensile strain of the strained silicon layer and to resist the formation of misfit dislocations that may be induced by temperature changes during processing. Consequently the critical thickness of strained silicon that can be grown on substrates having a given germanium content is effectively doubled. The silicon germanium layer overlying the strained silicon layer may be maintained during MOSFET processing to resist creation of misfit dislocations in the strained silicon layer up to the time of formation of gate insulating material.