The diffusivities of B, P, and As implanted in TiSi2are analyzed between 500 and 900 °C by secondary ion mass spectroscopy. It is shown that P and As have high (and almost equal) diffusivities compared with B which appears immobile. This difference is presumed to be related to the very high stability of TiB2(as compared with TiSi2) and the probable precipitation of B in the form of a titanium boride. The lattice diffusion coefficients for As and P are deduced from the diffusion profiles; they range from 10−17to 10−14cm2/s between 550 and 800 ° C. The activation energies are found to be, respectively, 1.8 and 2.0 eV; values close to the activation energy for the self‐diffusion of Si in TiSi2, 1.8 eV. The diffusion profiles also show a high grain boundary diffusivity and an accumulation of dopant at the TiSi2–Si interface.