Misfit dislocation arrays in In0.2Ga0.8As epilayers grown on GaAs substrates tilted 2°–10° away from exact (001) toward varied directions have been studied by transmission electron microscopy. A method has been developed to determine the glide plane and the Burgers vector of each misfit dislocation in the tilted InGaAs/GaAs interfaces. Based on experimental observations and theoretical analyses, it is proposed that a stacking fault surrounded by a 30° partial is at first generated by a growth error, followed by thermally activated nucleation of a 90° partial dislocation that removes the stacking fault and forms a 60° dislocation. From the frequency of nucleation events versus the dislocation glide force, the energy barrier for dislocation nucleation of &agr; and &bgr; 90° partial dislocations was determined to be equal to 1.5 and 1.4 eV, respectively. ©1995 American Institute of Physics.