An experimental study is reported on the various effects produced by the baking steps normally used in processing positive photoresists for application in microelectronics. The particular material investigated is AZ1350J, made by the Shipley Company, Inc. The thermal effects are studied in terms of a newly modified model that characterizes the exposure and development processes in photoresist. The changes in performance of the photoresist as a result of prebake, post-exposure bake, and post-development bake are discussed and are related to the parameters in the model that govern exposure and development. The model is derived from physical rather than chemical measurements.