Platinum-activated tungsten oxide (Pt-WO(3)) films for highly sensitive hydrogen (H(2)) sensors were co-deposited using radio frequency (r.f.) sputtering with subsequent two-step heat treatments. The Pt-WO(x) films were annealed at 700 degrees C for 1 h and then thermally treated at 450 degrees C for 24 h or 48 h. The microstructure, crystalline phase and composition of the as-sputtered, annealed and thermally treated films were characterized with scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The sensors were tested for 30-200 ppm H(2) in air at different temperatures from 95 to 220 degrees C and with a relative humidity from 0 to 75%. The influences of Pt concentration and thermal treatment on the microstructure and the sensing performances of the Pt-WO(3) films are presented in this work. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.