The masking properties of nanometer scale polymethylmethacrylate (PMMA) features used for definition of sub-100-nm-wide bridges inInP/Ga0.25In0.75Astwo-dimensional electron gas heterostructures by wet etching were investigated. Bridges untreated after the development of PMMA showed very poor masking ability due to a substantial exposure by backward scattered electrons from the surrounding exposed areas. However, if the resist was post-baked after development at a temperature higher than the glass transition temperature,Tg,the masking properties were restored and wet etched nanobridges of a sufficient quality were obtained. The post-development bake temperature and time were optimized to provide enough resist “packing” and yet not to cause resist flowing resulting in unacceptable alteration of the pattern geometry.