The paper presents the results of investigation of self-assembled Ge islands growth on Si (0 0 1) at 700 degrees C and the evolution of islands parameters during annealing. Dissolution of Si in islands was revealed front the Raman scattering and the X-ray diffraction measurements. It was found that the content of Si in islands increased during annealing. This increase was shown to result in the changes of island sizes and island shape from "dome" to "pyramid".