We have determined the room-temperature diffusivity of self-interstitials and vacancies in Si. Silicon p+−n junctions were realized in n-type epitaxial Si wafers, having an O and C content ⩽ 1015/cm3, and implanted at room temperature with 2.5 MeV He ions to fluences in the range 1×109–1×1012/cm2. The junctions were reverse biased at −30 V, in order to embody the entire damage profile of the ion in the depletion layer, and in situ leakage measurements were performed during and just after implantation. It is found that the leakage current increases monotonically during implantation while, at the beam turn off, it decreases by about a factor of 2 for times as long as 1 day. Ex situ deep level transient spectroscopy measurements show that the main contribution to leakage current is due to the deep levels introduced in the band gap by phosphorous–vacancy and divacancy complexes. This allowed us to associate the leakage current reduction at the beam turn off to the recombination of vacancy-type complexes by residual free interstitials. When, for a fixed fluence, the ion flux is increased, an initial faster transient, lasting up to ∼1000 s, is observed and has been attributed to the annihilation of residual free vacancies. Diffusivity values of 1.5×10−15 and 3.0×10−13 cm2/s for interstitials and vacancies, respectively, have been achieved from the analysis of these data. © 1998 American Institute of Physics.