A kinetic model based on thermodynamical concepts has been investigated to determine the grain size and its surface area in heavily arsenic‐doped polysilicon for various arsenic concentrations, annealing times and annealing temperatures. Computer simulation technique has been used to determine the grain boundary self‐diffusion of silicon atoms. The numerical analysis of our results shows that the grain surface area increases with annealing time and annealing temperature, but decreases with arsenic concentration. Our theoretical predictions have been compared with the available experimental results. Copyright © 1991 WILEY‐VCH Verlag GmbH & Co. KGaA