The evolution of the He-implantation induced defect structure in SiGe/Si heterostructures is observed during in situ annealing at 650 and 800 °C within a transmission electron microscope. The He implantation and annealing results in the formation of He precipitates below the SiGe/Si interface, which at first show a platelike shape and subsequently decay into spherical bubbles. The coarsening mechanism of the He bubbles is revealed as coalescence via movement of entire bubbles. The nucleation of dislocation loops at overpressurized He platelets and their propagation into the heterostructure could be observed as well. We found distinctly different velocities of the dislocations which we attribute to glide and climb processes. The in situ experiments clearly show that the He platelets act as internal dislocation sources and play a key role in the relaxation of SiGe layers.