We report effects of post-annealing on Indium Tin Oxide (ITO) thin films by their physical, electrical, optical, and electronic properties. Carrier concentrations increase up to annealing temperatures of 400 C, and then decrease at higher annealing temperatures. Burstein-Moss effect occurs as a function of annealing temperature with the highest optical bandgap of 4.17 eV achieved at 400 C. X-ray photoelectron spectroscopy revealed a 0.3 eV shift in the Fermi level of the annealed ITO films at 400 C, and the shift was reduced for temperatures higher than 400 C. In addition, the results of curve-fitting for the core levels showed a change of ratios of Sn02 and oxygen in the oxygen deficient regions after annealing. This is correlated to the change of carrier concentration and optical bandgap in the ultraviolet and near-infrared regions at different annealing temperatures. (C) 2014 Elsevier B.V. All rights reserved.