Abstract: Disclosed is a chemically amplified radiation sensitive composition containing a hydroxystyrene resin and an onium salt precursor which generates a fluorinated alkanesulfonic acid as a photoacid generator, wherein the photoacid generator is a sulfonium or iodonium salt of a fluorinated alkane sulfonic acid, represented by formula (I): Y+ASO3−  (I) wherein A represents CF3CHFCF2 or CF3CF2CF2CF2; and Y represents wherein R1, R2, R3, R4, and R5 each independently represent an alkyl group, a monocyclic or bicyclic alkyl group, a cyclic alkylcarbonyl group, a phenyl group, a naphthyl group, an anthryl group, a peryl group, a pyryl group, a thienyl group, an aralkyl group, or an arylcarbonylmethylene group, or any two of R1, R2, and R3 or R4 and R5 together represent an alkylene or an oxyalkylene which forms a five- or six-membered ring together with the interposing sulfur or iodine, said ring being optionally condensed with aryl groups.