Positive photosensitive resin composition and method of forming cured film from the same

A positive photosensitive resin composition comprising (A1) a resin containing any of structural units of general formula (1) below, which resin is insoluble in alkali or sparingly soluble in alkali but when its acid-dissociative group is dissociated, becomes soluble in alkali;

• (A2) a polymer or copolymer containing a structural unit derived from a radical-polymerizable monomer containing an epoxy group;
• (B) a compound containing two or more epoxy groups in its molecule, provided that the polymer or copolymer (A2) is not included in this compound;
• and (C) a compound that when exposed to actinic rays of 300 nm or longer wavelength, generates an acid,
• in which
• R1 represents a hydrogen atom, a methyl group, a halogen atom or a cyano group,
• each of R2 and R3 independently represents a hydrogen atom, or a linear alkyl group, provided that R2 and R3 are not simultaneously hydrogen atoms, and
• R4 represents a linear, branched or cyclic alkyl group or an aralkyl group, wherein the alkyl group is optionally subtituted with an alkoxy group having 1 to 5 carbon atoms or a halogen atom,
• provided that R2 and R4 may be linked to each other to thereby form a cyclic ether.