While dopants implanted in well annealed WSi2 show no lattice diffusion and only limited grain-boundary diffusion at temperatures up to 900 °C, on the contrary, rapid diffusion is observed at temperatures as low as 300 °C when the implantation takes place in the as-deposited amorphous silicide. Diffusion appears to be always accompanied by crystallization, although the inverse is not true: in particular, the diffusion of Sb occurs only at temperatures in excess of what is necessary to cause crystallization. The diffusion coefficients vary in reverse proportion to the size of the diffusing atoms, so that approximately equal coefficients for B, P, As, and Sb require respective temperatures of 350, 400, 450, and 500 °C. The diffusion coefficient of As at 500 °C is estimated at 1 × 10−14 cm2 s−1. The apparent activation energy for grain-boundary diffusion is close to 2.4 eV for P, As, and Sb.