B-doped polycrystalline Si films were prepared by electron beam evaporation and heat treatment in order to study the influence of B concentration and annealing temperature on recrystallization of polycrystalline Si. By using cross-sectional transmission electron microscopy and Auger electron spectroscopy it is shown that: (1) at a B concentration between 1 and 10 at. %, post-annealing at 1100 °C results in an enhanced solid phase epitaxial growth; (2) at a B concentration higher than 10 at. %, post-annealing results in a retarded recrystallization of polycrystalline Si; (3) a relatively stable amorphous alloy can form at a B concentration of ∼35 at. % up to 1100 °C. The mechanisms of the enhancement and the retardation are discussed.