High resolution masked ion beam lithography (MIBL) is demonstrated at large mask‐to‐sample gaps using two new types of membrane stencil masks. Single layer Si‐rich silicon nitride (SiN) membranes and Si3N4‐SiO2‐Si3N4(N‐O‐N) sandwich structure membranes are deposited by processes which allow the stress in the films to be adjusted. Transmission holes are reactive‐ion etched entirely through the membranes. This type of stencil mask virtually eliminates mask‐induced scattering. Lines and spaces of 160 nm have been exposed in 0.5‐&mgr;m polymethylmethacrylate (PMMA) at gaps as large as 275 &mgr;m, using 100‐keV protons. Some of the stencil mask limitations are overcome by multiple exposures. The results suggest that MIBL can be an extremely high resolution proximity printing technique.