In situ resistivity measurements, X-ray diffraction, 4He+ megaelectronvolt backscattering and Auger electron spectrometry were used to investigate the effect of oxygen diffusion on the electrical properties of a thin titanium film deposited onto silicon and heated at temperatures below 500°C. The annealing was performed in a vacuum of 10-5 Pa and in a hot purified helium furnace. The vacuum-annealed samples show a sharp increase in resistivity around 300°C. The increase is not due to silicon diffusion but is attributed to oxygen contamination. The presence of oxygen deforms the hexagonal structure of the titanium; the bond length along the c axis increases proportionally to the resistivity of the film. Annealing at temperatures higher than 500°C promotes silicide formation. The oxygen contained in the titanium film is segregated towards the outermost surface.