The onset of misfit dislocation generation in [001] In0.2Ga0.8As/GaAs single heterostructures is investigated by transmission electron microscopy using the liftoff technique. To determine the equilibrium critical thickness of misfit dislocation generation for different temperatures, postgrowth annealing was carried out for 2 h at 530 and 600 °C. The equilibrium critical thicknesses are determined as 100–120 A˚ for 530 °C postgrowth annealing and 60–80 A˚ for 600 °C postgrowth annealing, respectively. Metastable dislocation structures can be disturbed by sustained elevated temperatures. The variability in the effect is once again due to variations in the extent of dislocation pinning. ©1996 American Institute of Physics.