Tantalum silicide deposited directly on monocrystalline silicon substrates and annealed at 950 °C causes enhanced diffusion of both boron and antimony in buried layers. The effect is taken as evidence of vacancy supersaturation, since it is known that antimony diffuses in silicon by an almost entirely vacancy mechanism. It also indicates a substantial vacancy component in boron diffusion, at least at 950 °C, or lower. The simultaneous occurrence of boron and antimony enhanced diffusion contrasts with the nitridation effect on diffusion previously reported. That the enhanced diffusion occurred in buried layers excludes the snow‐plow mechanism. The Si:Ta ratio of the sputter‐deposited tantalum silicide is slightly less than 2. The interpretation is that further silicidation generates vacancies by removing silicon atoms from the silicon substrate. Enhanced diffusion was not detectable when there was a 150‐nm intervening layer of polycrystalline silicon film between the silicide and the monocrystalline silicon substrate, indicating that polycrystalline silicon is an effective sink for excess vacancies, perhaps more than it is for excess interstitials.