The resist performance of polymethacrylonitrile (PMCN) was tested with respect to applications in x‐ray lithography by irradiating the polymer with x rays (λ: 0.2–1.5 nm) generated by the electron storage ring BESSY. Both radiation sensitivity and contrast were greatly improved by soaking the irradiated polymer films with a very weak solvent (e.g., diethylketone) prior to development. Fine structure features of 0.3 μm (lines and spaces) were obtained at exposure doses of about 200 mJ/cm2using a mixture of cyclohexanone,o‐xylene, and water (weight ratio 65:34:1) as developer. PMCN performed quite satisfactorily in anisotropically operating etch resistance tests using a CHF3/O2plasma. The ratio of etch rates for PMCN and SiO2was determined asRPMCN/RSiO2<0.8. The resist performance of PMCN was independent of the initial molecular mass and the initial molecular mass distribution of the polymer in the rangeM=1×105–2×106.