W1-xSix (W0.90Si0.10 and W0.86Si0.14) films are deposited on SiO2/Si substrates by cosputtering from W and Si targets to form metal-oxide-semiconductor capacitors. After deposition, the samples are subjected to a thermal anneal at 700 degrees C in flowing N-2 ambient. Only body-centered-cubic W and/or beta-W are present in the W1-xSix films and no tungsten silicide can be found. However, the lattice constant of W is changed by adding Si and annealing treatment. Work functions of as-deposited W0.90Si0.10 and W0.86Si0.14 are 4.57 and 4.47 eV, respectively. After annealing at 700 degrees C, the work functions of W0.90Si0.10 and W0.86Si0.14 become 4.52 and 4.38 eV, respectively. The connection between the work function and material characteristics of W1-xSix is discussed. (C) 2008 The Electrochemical Society.