The selective deposition of tungsten films onto CoSi2 and onto Co by low pressure chemical vapor deposition and their material properties have been investigated with Auger electron spectroscopy, transmission electron microscopy, and Rutherford backscattering. When using WF6 and H2, uniformly thick tungsten films can be deposited onto CoSi2 without substrate alteration. In patterned structures, however, void formation was found at the perimeters of CoSi2 contacts to silicon, indicating encroachment of WF6 down the edge of the silicide‐Si interface. In WF6 and Ar, the film thickness was limited to 10 nm and some Si was locally consumed from the upper part of the CoSi2 film. Transmission electron diffraction showed evidence of Co2Si formation in these areas.