Different samples of poly(trifluoro‐2,2,2 ethyl methacrylate), made either by radical or by anionic copolymerization, with molecular weights ranging from 100 000 to 700 000 g mol−1have been investigated as positive x ray and electron resist. The best sensitivity and contrast have been found for the sample with the lower polydispersity index and the higher molecular weight in optimized developing conditions. Furthermore, we have found that in optimized developers, the ratio of molecular weights before and after irradiation, with a dose corresponding to the total dissolution of the film, is nearly a constant. The best resolution (0.5 μm for line and space gratings in a film of 0.6 μm thickness) has been obtained when development is carried out at low temperature (5 °C) in an appropriate solvent–nonsolvent mixture.