Relaxation of strained layer systems is still not well understood. It is time dependent and changes considerably for samples with different growth history. This has to be discussed in terms of nucleation, glide velocity and blocking of misfit dislocations. We have investigated these phenomena at samples with SiGe layer thicknesses ranging from 60 nm up to 120 nm grown by molecular beam epitaxy (MBE) or chemical vapor deposition (CVD) by means of X‐ray topography. The samples were annealed at temperatures between 500° and 600° C. Nucleation of misfit dislocations is heterogeneous and the rate is obviously dependent on layer strain and thickness. A quantified nucleation rate was not yet accessible, mainly due to the preferential formation of dislocation bundles. The propagation velocities of misfit dislocation segments were measured during annealing by means of synchrotron radiation plane wave topography (reflection geometry). The values agree well with theory and there is no evidence that they depend on growth regime. It is shown that the interaction of propagating misfit dislocations with crossing ones may lead to blocking or cross slip in different glide systems. These results are corroborated by investigations with atomic force and transmission electron microscopy.