Effect of carrier gases like argon, helium, and hydrogen on the deposition rate and properties of CVD tungsten from WF6-SiH4 was studied. Each carrier gas has different momentum and thermal diffusivity, and the mean free path and mass diffusivity of reactant molecules are also different. This has a significant effect on the deposition rate, film composition, and film morphology. A carrier gas with high thermal diffusivity high molecular velocity like helium lowers the deposition rate considerably because gas-phase formations of intermediate species, which go out of the reactor, are favorable. The film looks like powdery aggregates and shows poor adhesion. Effect of the carrier gases on the step-coverage, grain size, chemical composition, and electrical resistivity was identified from the experiment.