High quality InSb epitaxial layers were grown on GaAs substrates by metalorganic chemical vapor deposition using a two-temperature growth procedure. Trimethylindium and triethyl- or trimethylantimony were used for the growth of InSb on GaAs. Transmission electron microscopy revealed the existence of a large number of misfit dislocations at the substrate-epitaxial layer interface and, in some samples, misoriented grains. The quality of the layers improved with thickness as indicated by transmission electron microscopy, X-ray rocking curve widths and Hall mobilities. The mobilities were correlated with surface roughness, X-ray rocking curve width and the Sb/In ratio. Hall mobilities up to 60,900 and 27,900 cm2/V.s were obtained at 300 and 77 K. respectively, on a 2.9-mu-m thick InSb layer.