The interdiffusion in SiGe alloys has been studied by X-ray specular reflectivity using ex-situ and in-situ annealing experiments. We report on the evolution of the Ge profile of strain-compensated Si/SiGe multilayers due to high temperature annealing. These multilayers were grown pseudomorphically and strain-symmetrized on relaxed Si 0.75 Ge 0.25 and Si 0.5 Ge 0.5 pseudosubstrates by molecular beam epitaxy at 330 °C. The multilayer structures were annealed at several temperatures around 590 °C and around 800 °C. From modelling the X-ray specular reflectivity scans at various stages of the interdiffused structures, we obtained interdiffusion coefficients resulting in the activation energy and the prefactor for interdiffusion corresponding to Si 0.75 Ge 0.25 and Si 0.5 Ge 0.5 . The results obtained ex-situ for Si 0.5 Ge 0.5 and in-situ for Si 0.75 Ge 0.25 provide accurate values of diffusion parameters. 2442 M. Meduň a et al.: Interdiffusion in SiGe alloys with Ge contents of 25% and 50%