Non-conventional chemically amplified (CA) resist was designed. Photo-induced thiol/ene radical reaction was used to insolubilize the resist based on multifunctional thiol and poly(4-hydroxystyrene) (PHS) derivatives. Hydroxy groups of PHS were modified with allyl or propargyl moiety. Dissolution property of the modified-PHS in TMAHaq solution was affected by the modification degree. Resist was prepared by mixing the modified-PHS, multifunctional thiol compound, and photoradical generator. Photosensitivity of the resist was studied at 254 and 13.5 nm. The sensitivity was strongly affected by the modification degree of PHS, molecular weight of PHS, molecular weight distribution of PHS, amounts of thiol compound and photoradical generator added. It was found that the present resist system was highly sensitive to EUV exposure.