AbstractA model of high‐energy ion implantation is formulated with allowance for fluctuations of the charge state of ions and the corresponding backward transport equation for post‐implantation spatial distributions of an impurity. Simulation results of experiments concerned with boron ion implantation into silicon by numerical solving the backward transport equation are reported. It is shown that the account of ion charge fluctuations in the high‐energy range leads to an increase of the range straggling of the implanted impurity and provides a better agreement with the experiment than the traditional methods of modelling based on the use of the Monte‐Carlo method or the backward transport eq