Films of the type used for see‐through masks dissolve much more slowly in after irradiation with the electron beam of a scanning electron microscope. The ratio of the time to dissolve irradiated material to the time to dissolve unirradiated material is 25 or greater. The films behave, therefore, as negative resists. Irradiation studies were conducted over a voltage range of 5–30 kV, a current range of , and scanning rates in the range 1–500 mm/sec. On glass substrates at room temperature a minimum current of is required at a beam diameter of approximately 1 µm. At , flakes from the substrate thus establishing a practical maximum current for the process. In general, the line width of the made insoluble increases with, increasing voltage and decreases with increasing scanning rate. For a scanning rate of 500 mm/sec and a beam current of , a line width of 0.8 µm is obtained. Edge definition is excellent. Transmission electron microscopy shows the irradiated, insoluble part of the film to be a mixture of and . Similar results are obtained for films deposited onto oxidized silicon and silicon, although the latter requires a somewhat higher threshold current. Use of this process is suggested for direct construction of see‐through masks without intermediate steps involving organic resists. Because of their dimensional and thermal stability, resist films should also be useful as masks for processes involving high temperatures. These include ion implantation, sputtering, and possibly dopant diffusion.