This paper concerns a novel three-component chemically amplified positive tone resist system for EB lithography composed of a novolak resin, an acid generator, and a newly synthesized dissolution inhibitor. To obtain resist materials with high sensitivity and high contrast, the authors synthesized four 1-(3H)-isobenzofuranone derivatives as novel dissolution inhibitors was effectively decomposed by an acid catalyzed thermal reaction. In addition to this decomposition, the lactone ring of the decomposed product was spontaneously cleft in an aqueous base to generate carboxylic acid. Among these synthesized substances, only the t-Boc derivative of o-cresolphthalein, named CP-TBOC, showed an excellent solubility in 1-acetoxy-2-ethoxyethane. The subsequent cleavage in an aqueous developer was investigated by UV-visible spectroscopy.