Abstract: A positive photoresist composition is disclosed, comprising (a) from 50 to 99 parts by weight of a polyhydric phenol compound which is a condensation product between a mixed phenol comprising o-cresol and at least one of 2,5-dimethylphenol and 3,5-dimethylphenol at a molar ratio of from 95/5 to 5/95 and an aldehyde and (b) from 1 to 50 parts by weight of a quinone diazide compound. The composition is excellent in sensitivity, resolving power, heat resistance, and resistance to dry etching.

Abstract: Orthocresol or a mixture of orthocresol and paracresol and an aldehyde compound or a derivative thereof are subjected to polycondensation in a solvent selected from an aliphatic alcohol having 3 to 12 carbon atoms, a glycol ether having 3 to 6 carbon atoms, benzyl alcohol and an aliphatic carboxylic acid having 2 to 6 carbon atoms, in the presence of an acid catalyst, to obtain linear and high molecular weight orthocresol-novolak resins or orthocresol/paracresol random copolymerized novolak resins which have a high softening point of 145.degree. C. or higher and a high number average molecular weight of 1500 or more and which are highly soluble in alcohols and ketones and are highly compatible with resins.