Polyphthalaldehyde (PPA) inhibits dissolution of novolac resins in aqueous base very efficiently. When an onium salt cationic photoinitiator such as triarylsulfonium or diaryliodonium metal halides is added to the polymer mixture, PPA is completely reverted to the starting monomer by reaction with radiochemically generated acid and removed from the exposed area upon postbake, thereby recovering the intrinsic base solubility of the novolac resin. PPA as a polymeric dissolution inhibitor used in conjunction with onium salts provides aqueous-base-developable, high-contrast, positive resist systems very sensitive to deep UV radiation (full development at 2 mJ/cm2). The system offers stable development processes due to the induction effect and high contrast. © 1988, The Electrochemical Society, Inc. All rights reserved.