Insitureflection high‐energy electron diffraction and cross‐sectional and plan‐view transmission electron microscopy have been used to investigate the initial stages of InSb growth on GaAs(001), by molecular‐beam epitaxy. Growth of the InSb commences with the formation of rectangular‐based islands, having flat tops and sloping sides, with facets on certain planes of types {111} and {113}. The islands show near normal lattice spacings, with no significant straining. As deposition proceeds, islands coalesce and, after the equivalent of 40 monolayers of deposition, form a connected network. Complete coverage of the GaAs substrate is achieved after &bartil;300 monolayers of deposition. This places a lower limit on the thickness of InSb layers, which may be considered in the design of optoelectronic devices.