Abstract: A model is proposed that describes variation of the shape of nanoislands grown by method of selective epitaxy. The model is based on minimization of the system surface energy at a given volume. In terms of the adopted morphology, the island is bounded by (101) and (112) side facets and a (001) top facet with varying dimensions dependent on the volume. Areas, lengths, and aspect ratios of competing facets are calculated as functions of the island volume.