A new family of highly sensitive resists for deep-UV, x-ray, and electron-beam exposure capable of better than 100 nm resolution and very high pattern aspect ratio has been investigated. The resists are based on epoxidized novolac resins sensitized with acid-generating compounds. Upon exposure to ionizing radiation, strong acids are formed which, during a subsequent bake, cause crosslinking of the resin by epoxide ring opening. Formulations made with purified and fractionated commercial resins show extremely high e-beam sensitivity, up to 0.2 |μC/cm2 at 20 kV and 0.5μC/cm2 at 50 kV with pattern aspect ratios higher than two and resolution better than 0.25 μm lines and spaces. © 1991, The Electrochemical Society, Inc. All rights reserved.