Lateral epitaxial overgrowth of GaSb on GaSb and GaAs substrates patterned with SiO2 or Si3N4 films by metalorganic chemical vapor deposition was accomplished using trimethylgallium and trimethylantimony. Transmission electron microscopy measurements show that coalesced films grown on GaSb substrates exhibit defect-free materials, while those on GaAs substrates show regular, small-angle crystal tilting originating from large lattice mismatch.