Islands of InAs were fabricated at various temperatures by Stranski-Krastanow growth of the molecular beam epitaxy and were observed by the atomic force microscopy. The island size increased and the island density decreased with an increase in temperature. The change was caused by an increase in the migration length of In adatoms with increasing temperature. An Arrhenius plot of the island density showed a linear tendency and agreed with the results Of other works. For understanding the results, an expression for island density was obtained on the assumption that the density is saturated under constant In flux and In atoms do not detach themselves from the islands. Using the expression, the activation energy for migration of an In adatom was estimated to be 4.0 eV from the Arrhenius plot. The activation energy was discussed based on another theoretical expression also. (C) 2002 Elsevier Science B.V. All rights reserved.