In2O3 (111) single-crystalline films have been grown on sapphire (0001) substrate by RF plasma-assisted molecular beam epitaxy. The epitaxial relationship between the film and substrate was determined by in situ reflection high-energy electron diffraction, ex situ Xray diffraction and transmission electron microscopy. Optical and electrical measurements show that the undoped In2O3 films are highly transparent and conductive. Twin crystals were observed as the main defects in the film by high-resolution electron microscopy. The film may be used for transparent electrical contact in optoelectronic devices, such as ZnO-based ultraviolet diodes and lasers. (c) 2006 Elsevier B.V. All rights reserved.