Gravimetric and SIMS analyses of vacuum‐deposited Ta films on Si substrates as well as films obtained by their thermal oxidation demonstrate a significant interaction in structures well below the usual temperatures required to form or on silicon. The interaction begins during the deposition of the Ta film, leading to the incorporation of silicon in the film. It is suggested that oxygen gettered by tantalum facilitates this process. During oxidation of the Ta film, the silicon in the film is cooxidized and oxygen diffusing through the already formed oxide enhances the further entry of silicon into the film. Oxygen diffusing through the completely oxidized Ta film further reacts with the silicon substrate during postoxidation heat‐treatment in oxygen. There is no evidence that the interaction during any of these three steps is caused by intermixing elemental tantalum and silicon. The results of gravimetric and SIMS analyses are qualitatively consistent with the measured dielectric parameters of the film and the observed electronic properties of the interface.