Data are presented on the mechanical stress σ developing in the diffusion zone of gallium arsenide single crystals at different dislocation densities and relationships between the concentrations of arsenic and gallium vacancies. The results are analyzed in terms of impurity diffusion through gallium, arsenic, and interstitial sites. The influence of the defect system on σ is shown to depend on the mechanism of impurity diffusion. A correction coefficient which eliminates the discrepancy between experimental stress data and theoretical predictions is determined for different diffusion mechanisms.