A method of forming a relaxed silicon—germanium layer for use as an underlying layer for a subsequent overlying tensile strain silicon layer, has been developed. The method features initial growth of a underlying first silicon—germanium layer on a semiconductor substrate, compositionally graded to feature the largest germanium content at the interface of the first silicon—germanium layer and the semiconductor substrate, with the level of germanium decreasing as the growth of the graded first silicon—germanium layer progresses. This growth sequence allows the largest lattice mismatch and greatest level of threading dislocations to be present at the bottom of the graded silicon—germanium layer, with the magnitude of lattice mismatch and threading dislocations decreasing as the growth of the graded silicon—germanium layer progresses. In situ growth of an overlying silicon—germanium layer featuring uniform or non—graded germanium content, results in a relaxed silicon—germanium layer with a minimum of dislocations propagating from the underlying graded silicon—germanium layer. In situ growth of a silicon layer results in a tensile strain, low defect density layer to be used for MOSFET device applications.