The behavior of monolayer‐deep holes on the surface of (001) GaAs grown by molecular beam epitaxy during post‐growth annealing is observed byinsituscanning electron microscopy. Most small holes disappear immediately after growth in the same way as the islands. However, it is found that some are left for a long time and form big holes with each other. These residual big holes are elongated in the [110] direction initially. They extend in the [110]direction and coalesce with each other, but, at the same time, they shrink in the [1–10] direction and become elongated in the [110]direction. Finally they shrink in both directions and disappear. It takes about 10 min for all the holes to disappear, which is much longer than the growth interruption period usually employed to smooth heterointerfaces. The anisotropic behavior of big holes are discussed in relation to the reported growth anisotropy.