Lateral distributions of damages introduced in semiconductors by the ion-implantation are theoretically studied using the theory of Lindhard etal. As a result, it is found that the lateraldamage distribution formed by a single implanted ion can be approximated by a gaussian, and that the lateral damage spread is laraest near the ion projected range depth. In the case of the ion-implantation through a mask-window, it is also found that the lateral damage distribution formed by many ions can be extpressed bv a compllementary error function near the mask eage,and that the lateral damage spread from the mask edge is smaller than the damage spread along the depth direction even in the case of light ion implantation such as B+ into Si. It can be concluded that the lateral ion enhanced diffusion would be smaller than the depth enhanced diffusion.