Square surface defects evolving in a triangular shape were observed on Si(0 0 1) as the consequence of long annealing step at very high temperature and in slightly oxidizing conditions. The evolution of the size and shape of these defects were studied as a function of time, of surface misorientation and of oxygen/neutral gas ratio. The association of the Burton Cabrera and Frank (BCF) model developed for ultra high vacuum conditions with the Deal and Groves (DG) law for oxidation allows to explain the influence of the studied parameters on the defect evolution. This shows that the oxidation step proceeds with the help of diffusion along the interface rather than with a localized reaction, at least in the conditions of the experiment. (C) 2003 Elsevier B.V. All rights reserved.