The effect of the growth conditions on halide vapor phase epitaxy of In2O3 on sapphire (0 0 0 1) substrates was investigated. Only the most thermally stable phase c-In2O3 grows at growth temperatures of 400 to 1000 degrees C. The growth rate increased as the growth temperature increased up to 700 degrees C, and layers with rough surfaces and a preferred (100) orientation were grown. Above 700 degrees C, the growth rate became constant, the preferential orientation changed to (111), and layers with smooth surfaces were grown. At 1000 degrees C, the volume fraction of the (111)-oriented domains in the grown layer reached 99.0%, although there were in-plane twins rotated by 180 degrees. The growth rate also increased as the input partial pressure of the InCl or O-2 source gas was increased, and a high growth rate exceeding 10 mu m/h was found. The layer grown at 1000 degrees C was of high purity and incorporated no impurities other than Cl. Optical transmission measurements of this layer showed high optical transmittance at energies below the optical gap of 3.47 eV.