A new lithographic technique will be described in this paper which makes it possible to increase the height‐to‐width (aspect) ratio of electron‐beam‐exposed patterns in the resist layer, without significantly increasing proximity effects. The technique consists of applying two resist layers on the substrate, separated by a thin metal film. The pattern is electron‐beam exposed on the top resist layer, and after development, a thin (2000–3000 A) gold or other x‐ray absorbing material is used to form an in situ x‐ray mask to expose a much thicker bottom resist layer in an x‐ray exposure system. It is shown that with this technique, lines of 0.25‐μm wide with vertical walls, can be obtained in 2‐μm‐thick PMMA resist or an aspect ratio of eight can be easily achieved. It is also shown that the in situ mask can be registered to a previous level on the workpiece with accuracy better than 0.1 μm.