Abstract Diffusion of tellurium in monocrystalline silicon was investigated in the temperature range 1149 K–1653 K. The radiotracer 121Te originated from production, on-line implantation and subsequent decay of its grandmother isotope 121Xe at the ISOLDE facility of CERN. Penetration profiles were measured by means of mechanical sectioning after long-time diffusion annealing. Te concentrations down to 10 16m −3 could be detected. An Arrhenius plot of the measured diffusivities reveals a pronounced curvature. This is interpreted in terms of two diffusion processes each of which is characterized by its own activation energy and pre-exponential factor. In the low temperature regime Te transport takes place through the vacancy (V) mechanism. Above about 1500 K, interstitial-substitutional diffusion becomes predominant. The latter component most probably arises from self-interstitials (I) participating via the kick-out reaction. From the present data the fractional V- pr I-component of Te diffusion under point-defect equilibrium can be calculated for any temperature.