We have developed a method, anodization controlled miniaturization enhancement (ACME), to make ultrasmall tunnel junctions. Anodization of electron‐beam fabricated Al/Al2O3/Al tunnel junctions reduces their effective areas and capacitances, which realizes single electron transistors operating at high temperatures up to nearly 30 K. The limit of the increase in the charging energy is attributed to the initial scattering in the junction sizes. ©1996 American Institute of Physics.