We have studied both experimentally and theoretically the generation of damage in GaAs due to ion implantation through mask openings of small dimensions. We show that it is possible to master the generation of damage, i.e., the amorphization phenomenon in the direction perpendicular to the ion beam and close to the mask edges. A theoretical model is used to simulate the ion implantation process and damage accumulation through Ti–Au masks. After comparing the shape of the crystalline/amorphous interfaces as revealed by cross‐sectional electron microscopy with our simulations, this model is used to predict the evolution of the two‐dimensional damage distributions beneath the mask edges as functions of ion beam and implantation mask parameters. Undamaged regions of nanometer dimensions can be preserved even when using masks of reasonable dimensions (100–200 nm). This can be done only by adjusting the ion beam parameters through the accurate simulation of the two‐dimensional damage generation. ©1996 American Institute of Physics.