Insitux‐ray topography is used for the study of misfit dislocations in growing heteroepitaxial layers. Topograms taken from Ge layers on GaAs substrates show the generation of misfit dislocations at various locations commencing at a layer thickness of about 1000 A˚. These dislocations elongate and eventually grow to a dense cross‐grid array. The specially designed epitaxial reactor and the topographic arrangement with a time resolution between 2 and 20 sec are briefly described.