Abstract: A method for implanting diffusion regions during production of MOS transistors involves first patterning and etching a gate to produce a resist overhang covering at least one edge of the gate. Primary dopant is then implanted in the substrate to produce a first diffusion region having at least one boundary partially defined by the resist overhang covering the gate. By isotropically etching the resist on the gate, the gate itself is used as a mask during subsequent implantation of a halo diffusion region. The size of both the first diffusion region and the halo diffusion region is subsequently adjusted by annealing.