Molybdenum oxide (MoO3) films were deposited on glass and (1 1 1) silicon substrates by sputtering of metallic molybdenum target in an oxygen partial pressure of 2 x 10(-4) mbar and different substrate temperatures in the range 303-623 K using dc magnetron sputtering technique. X-ray photoelectron spectrum of the films formed at 303 K showed asymmetric Mo 3d(5/2) and Mo 3d(3/2) peaks due to the presence of mixed oxidation states of Mo5+ and Mo6+ while those deposited at substrate temperatures >= 473 K were in Mo6+ oxidation state of MoO3. The films formed at substrate temperatures >= 473 K were polycrystalline in nature with orthorhombic alpha-phase MoO3. Fourier transform infrared spectra of the films showed an absorption band at 1000 cm(-1) correspond to the stretching vibration of Mo=O, the characteristic of the alpha-MoO3 phase. The electrical resistivity increased from 3.3 x 10(3) to 8.3 x 10(4) Omega cm with the increase of substrate temperature from 303 to 473 K respectively due to improvement in the crystallinity of the films. Optical band gap of the films increased from 3.03 to 3.22 eV with the increase of substrate temperature from 303 to 523 K. (C) 2009 Elsevier B.V. All rights reserved.