ABSTRACT Heat and mass transfer devices are being fabricated by International Mezzo Technologies that utilize micro features with increasingly aggressive combinations of both feature height and feature aspect ratio. Improvements in x-ray lithography using SU-8 now make it possible to lithographically define densely packed arrays of features with heights of 3 mm and with aspect ratios of around 25. These arrays potentially serve as the starting point for increasingly aggressive LIGA-based micro machining of heat exchangers, regenerators, recuperators, etc. that have superior performance due to length scale advantage