The annealing effects on the electrical properties and microstructures of indium oxide (In(2)O(3)) thin films were investigated. The In(2)O(3) thin films with the thickness of about 150 nm were annealed at various temperatures ranging from 100 to 600 degrees C in air after the sputtering deposition. It was found that the carrier density of the In(2)O(3) thin films decreased with increasing in the annealing temperature and then started to increase at a certain temperature. This indicated that the reduction of the In(2)O(3) thin films was promoted at high annealing temperature. The Hall mobility of the In(2)O(3) thin films increased through the reduction; furthermore, the d-spacing of the In(2)O(3) crystal lattice plane tended toward ideal value. It can be believed from these results that one of the principal electron scattering in the In(2)O(3) thin films is attributed to excess oxygen atoms that expand the d-spacing. (C) 2011 Elsevier B.V. All rights reserved.