Abstract: The transformation of micropits on large terraces of the Si(111) surface containing no vicinal atomic steps has been investigated by in situ ultrahigh-vacuum reflection electron microscopy upon thermal annealing of the substrate in the range of 1200–1400°C. A procedure for the formation of micropits on large terraces of the Si(111) surface with the application of focused-ion-beam (Ga + ) technology has been proposed. It has been found that the micropit decay kinetics varies upon reaching the critical radius R crit , which is caused by the activation of nucleation of two-dimensional vacancy islands on the micropit bottom. A theoretical model describing variations in the lateral sizes of the micropit both before and after reaching R crit has been proposed. Based on analysis of the found temperature dependence of the nucleation frequencies of two-dimensional vacancy pits on the micropit bottom, the effective energy of nucleation of a vacancy island has been determined to be 4.1 ± 0.1 eV.