SiGe/SOI films have been investigated by transmission electron microscopy (TEM), atomic force microscopy (AFM) and Raman spectroscopy. For low Ge composition (∼ 20%), strain relaxation in the SiGe layer is minimal (<0.25%). For higher Ge content (32%), the tensile strain in a Si capping layer grown on top of SiGe/SOI is 0.46% (a stress of 0.81 GPa). TEM has revealed that most of the resulting defects at the SiGe/SOI interface and move downward. The misfit dislocation (MD) linear density is 17/μm, being consistent with the strain relaxation of the SiGe layer as determined by Raman spectroscopy. Upon thermal annealing, residual strain in the SiGe films has been further relaxed via two major routes (a) introduction of more MDs, and (b) development of surface undulation. High strain relaxation has been achieved in a SiGe layer grown on a higher-Ge content buffer layer.