We have investigated lateral In–In pair correlations within the wetting layers of buried InAs/GaAs quantum dots imaged with cross-sectional scanning tunneling microscopy. We quantified the number of In–In pairs along the  direction as a function of the spacing between them. Since the number of In–In pairs exceeds that of a randomly generated distribution of In atoms, significant lateral In clustering within the wetting layers is apparent. A comparison of the experimentally determined and randomly generated In–In pair distributions reveals nearest-neighbor In–In pair interaction energies similar to those calculated for InGaAs alloy surfaces [J. -H. Cho, S. B. Zhang, and A. Zunger, Phys. Rev. Lett. 84, 3654 (2000)]. The In–In pair correlations increase with high temperature annealing, indicating that vertical In–Ga interdiffusion occurs simultaneously with lateral In segregation. Together, these results suggest that initial In clustering in the wetting layer may be frozen at the surface during growth, and that annealing increases the effective sizes of these clusters, driving the system toward its segregated equilibrium state. © 2002 American Institute of Physics.