The growth and optical band gaps of heteroepitaxial layers of the ternary In1−xGaxSb [0≤x≤1] on (100)GaAs is reported. The epilayers, prepared by metalorganic magnetron sputtering using trimethyindium, trimethylgallium, and a sputtered antimony beam, showed good structural and surface morphologies despite a lattice mismatch between substrate and epilayer of 9%–14%. Secondary ion mass spectrometry analysis indicated a background carbon level in proportion to the gallium concentration. The high levels of carbon were not present in the InSb layers prepared using TMI. All films showed optical absorptions characteristic of direct gap semiconductors. The bowing parameter for the system is somewhat lower than that observed for the corresponding bulk material and may be related to compressive stress in the layers.