Chemical vapor deposition of WSi2was studied through thermodynamic equilibrium calculations for the W–F–Si–H and W–F–Si–H–Cl systems. The calculations were made with a computer program that minimizes the Gibbs free energy by Langrangian multiplier techniques. The parameter range for these system analyses were: temperature 473 to 1073 K, pressure from 50 to 500 mTorr, and Si/W ratios of 3 to 1000. 21 gas phase species and eight solid species were included in the calculations for the W–F–Si–H system and 39 gas phase species and 15 solid species were considered for the W–F–Si–H–Cl system. At the equilibrium condition, H2, SiF4, and SiF2H2are the most prominent gaseous species for the W–F–Si–H system while WSi2and Si are formed in the solid phase. For the W–F–Si–H–Cl system, WSi2and Si are formed in the solid phase, while H2, SiCl4, HCl, SiF4and SiHCl3are the most prominent gas phase species. The SiCl2intermediate plays a key role in the surface activated reaction for this system.