A series of transparent photochemical acid-generators (PAGs) has been successfully prepared and investigated to apply ArF excimer-laser lithography. These PAGs were synthesized as new alkylsulfonium salts that have cycloalkyl groups but no aromatic ones. They were almost transparent at 193. 4 nm and have high acid-generation efficiency enough to use for ArF excimer-laser resists. The photochemical reaction of these alkylsulfonium salts occurs mainly due to the S-C bond fission. A resist utilizing the PAGs was capable to resolve a 0. 2µm L/S pattern at a 50-mJ/cm2 dose with an aqueous alkaline developer. These PAGs are promising materials for use in ArF excimer-laser lithography.