The effect of the remaining solvent on the diffusion of the catalytically active acid within the chemical amplification resists is discussed. A range of solvents was investigated from the viewpoint of sensitivity, diffusion, and resolution. The solvent remaining after the coating and baking processes is thought to one of the most probable factors among the several possible causes in the determination of the performance of the resists. It is also considered to result in the environmental instability which is currently one of the most serious problems in the use of the resists of this type. The remaining solvent drastically enhances the thermal diffusion of acid generated from photo‐acid generators upon photoanalysis. The log of the diffusion range of the acid is found to be proportional to the concentration of the remaining solvent. This phenomenon may be described by a theory which combines the hole theory of liquids and the free volume theory of polymers and was also found to be the correlation energy between resin, solvent, and acid. In practice, this enhancement of diffusion range by remaining solvent does not result in higher sensitivity but rather degrades the performance of the resists.