A method of forming a substantially relaxed SiGe-on-insulator substrate in which the consumption of the sidewalls of SiGe-containing island structures during a high temperature relaxation annealing is substantially prevented or eliminated is provided. The method serves to maintain the original lateral dimensions of the patterned SiGe-containing islands, while providing a uniform and homogeneous Ge fraction of the islands that is independent of each island size. The method includes forming an oxidation mask on at least sidewalls of a SiGe-containing island structure that is located on a barrier layer that is resistant to Ge diffusion. A heating step is then employed to cause at least relaxation within the SiGe-containing island structure. The presence of the oxidation mask substantially prevents consumption of at least the sidewalls of the SiGe-containing island structure during the heating step.