We proposed and demonstrated a new approach to pressed self-perfection by liquefaction (P-SPEL), where a layer of SiO₂ is used as a stopper on one sidewall of gratings, to self-limit the final trench width in P-SPEL to a preset stopper layer thickness, allowing a precise control of the final trench width without the need to control any pressing parameters such as pressure, temperature and the gap between the pressing plate and the substrate. We achieved 20 nm wide trenches from a 90 nm original width, reducing the original trench by 450%. We also observed improvement in the trench width uniformity. Using the fabricated resist trenches as templates, 20 nm metal lines were achieved by lift-off.