Growth conditions of heteroepitaxial thin films of tin-doped Ga2O3 were surveyed from the viewpoint of visible application to field-effect transistors (FETs). Films were deposited by pulsed laser deposition, and post-annealing was examined to improve film structures. Atomically flat surfaces were obtained for films grown oil yttria-stabilized zirconia (III) plane and post-annealed at 1400 degrees C, but they were insulating. Conductive heteroepitaxial films applicable to FETs were obtained on alpha-Al2O3 (0001) at specific deposition conditions, i.e. substrate temperatures from 500 to 550 degrees C and oxygen pressures from 5 x 10(-4) to 1 x 10(-3) Pa. It was found that the resulting epitaxial films have a crystal structure different frorn that of beta-Ga2O3. The crystal lattice for the films is determined to be orthorhombic with a large possibility of a higher-symmetry hexagonal or rhombohedral system. The films exhibited high transparency in the near infrared-deep ultraviolet region and had bandgap of similar to 4.9 eV The operation of top-gate MISFETs using the Ga2O3 film for the n channel was demonstrated. (c) 2005 Published by Elsevier B.V.