Pr0.5Ca0.5MnO3 (PCMO) films were deposited on LaAlO3 (100) substrates changing process pressure from 1.33 to 5.33 Pa by RF magnetron sputtering. Current-voltage characteristic measurements and spectroscopic ellipsometry measurements were carried out to investigate the mechanism of resistance switching in PCMO films. Resistance switching was observed in the devices composed of the PCMO films deposited at low pressures of 1.33 and 2.67 Pa. The deposition pressure dependence of the electronic structure of PCMO films was detected as a difference in dielectric functions by spectroscopic ellipsometry. Spectroscopic ellipsometry data indicated that the PCMO films exhibiting resistance switching had large oscillator strength of the electric dipole charge transition in (MnO6)(9-) and (MnO6)(8-) octahedral complexes, small oscillator strength of d-d transitions in Mn3+ and Mn4+ ions, and large high frequency dielectric constant. The formation of (MnO6)(9-) and (MnO6)(8-) octahedral complexes and oxygen vacancies might be required for obtaining large resistance switching. (C) 2013 Elsevier B.V. All rights reserved.