This article presents the results of the experimental and modeling study of a positive tone, chemically amplified photoresist, in application to x‐ray lithography. Spectrophotometric titration, Fourier transform infrared spectroscopy (FTIR), and development rate monitor data were acquired and used as inputs for the modeling of the processes and pattern simulations. The exposure model assumes monomolecular decomposition upon radiation and corresponds to Dill’s model for a nonbleaching photoactive compound. The post‐exposure bake (PEB) model is based on formal kinetic equations which include a term for photoacid loss (or side reactions) during the post‐exposure bake process in a generalized way. The effective kinetic order of the photoacid loss reaction is derived from the FTIR absorbance data obtained for different PEB times and exposure doses. For patterned exposures, a diffusion term for the local photoacid concentration is included. The photoacid and tert‐butoxycarbonyloxystyrene concentration profile changes with PEB time have been simulated for a 0.25 μm line and spaces pattern. It is shown that a nonlinear PEB photoacid reaction kinetics, rather than the photoacid diffusion, dominates the linewidth decrease during PEB for the photoresist studied.