Self-aligned aluminum-gate MOSFET's have been successfully fabricated by employing ultraclean ion implantation technology. The use of ultra high vacuum ion implanter and the suppression of high-energy ion-beam-induced metal sputter contamination have enabled us to form ultra-shallow low-leakage pn junctions by furnace annealing at a temperature as low as 450. The fabricated aluminum-gate MOSFET's have exhibited good electrical characteristics, thus demonstrating a large potential for application to realizing ultra-high-speed integrated circuits.