The mechanisms for stress relaxation have been investigated during growth of InGaAs/GaAs heterostructures in a regime where misfit dislocations and surface morphology strongly interact. Real time stress evolution was obtained using an in situ multi-beam optical stress sensor measurement during molecular beam epitaxy of In0.2Ga0.8As on a semi-insulating GaAs(001) substrate misoriented 2degrees toward the [110] direction. This real time data was compared to analysis of data obtained from X-ray diffraction and atomic. force microscopy. Several distinct stages of the stress evolution were observed during growth that are correlated to the development of morphology and strain relaxation in these films. The stress evolution is divided in four regimes: pseudomorphic growth, slow strain relaxation, fast strain relaxation and saturation. The stress is initially relieved partially by widely spaced 3D features that develop on the surface. As the growth thickness continues beyond 900 Angstrom and the critical thickness for misfit dislocation formation is exceeded, a cross-hatch morphology overtakes the 3D morphology coincident with the rapid relaxation regime and dislocation formation. An instantaneous tensile stress appears during this stage of growth that is associated with the coalescence of the surface undulations created by the cross-hatch. (C) 2004 Elsevier B.V. All rights reserved.