A technique of introducing donor or acceptor impurities into a semiconductor to create n-type or p-type regions. The impurity atoms are ionized in a gaseous form, and then accelerated in a vacuum using a high potential and fired at the target semiconductor layer. The high-energy ions penetrate the surface of the semiconductor and rapidly come to rest in the solid. The average depth of the impurities in the semiconductor is a function of the accelerating potential, and so the depth of the doping can be carefully controlled. The number of ions implanted can be calculated from the current flow through the target, as the ions are neutralized, and the duration of the implantation process. Very carefully designed impurity profiles can be created using this process, which is used to make the very small transistors for high-speed, high-frequency, and VLSI integrated circuits.