Thermal transport in polymer layers is an important consideration in various lithography techniques, including immersion lithography and thermolithography. The in-plane thermal conductivity of commercially available photoresist AZ 5214E is determined at each stage of lithography processes using ultrathin (< 100 nm) freestanding membrane devices. The authors find that UV exposure does not lead to any appreciable change in thermal conductivity whereas cross-linking induced by postexposure bake results in a slight increase (similar to 5%). The thermal boundary resistance across interfaces between the resist layers and metal films/substrates is also found to be significant. The experimental techniques and data presented here will facilitate a systematic evaluation of thermal phenomena during lithography processes. (c) 2007 American Vacuum Society.