Tungsten silicide (W1-xSix, continuous increase in Si content ranging from 30 to 74 atom %) films are deposited on SiO2/Si substrates by cosputtering from W and Si targets. After deposition, the samples are subject to a thermal annealing at 900 degrees C to form crystalline silicide phases. With their almost stoichiometric compositions, 900 degrees C annealed W0.64Si0.36 and W0.31Si0.69 exhibit W5Si3 and WSi2 phases, respectively, while W0.44Si0.56 displays mixed phases of W5Si3 and WSi2. With excess W, W0.70Si0.30 film exhibits W5Si3 phase with a trace of body-centered cubic W. W0.26Si0.74 contains excess Si but shows a WSi2 phase of similar crystallinity to that of W0.31Si0.69. Work functions of 900 degrees C annealed W0.70Si0.30, W0.64Si0.36, W0.44Si0.56, W0.31Si0.69, and W0.26Si0.74 are extracted from the plot of flatband voltage vs SiO2 thickness of the related metal-oxide-semiconductor capacitors, and the values are 4.34, 4.31, 4.61, 4.76, and 4.72 eV, respectively. It is deduced that the work function of W1-xSix is mainly related with the phases, and their connection is discussed. (C) 2008 The Electrochemical Society.