Sub‐10 nm structures were fabricated by lift‐off and by etching following electron‐beam exposure of poly(methylmethacrylate) (PMMA) resist on solid semiconductor substrates. Electron beam lithography at 80 kV with a beam diameter smaller than 5 nm was used to expose PMMA resist on either Si or GaAs substrates. The exposed resist was developed with a 3:7 cellosolve:methanol mixture in an ultrasonic bath for 5 s followed by rinsing in IPA and blown dry with pure nitrogen. Ultrasonic agitation during development was found to be essential for forming sub‐10 nm structures in PMMA. The patterned PMMA resist was used either as a lift‐off mask or an etching mask and successful transfer of the pattern to the substrates was achieved. For lift‐off an ionized beam deposition method, which gives smaller grain size and better adhesion of the metal film to the substrate, was used to deposit a layer of AuPd. Metal dots with sub‐10 nm diam and metal structures with sub‐10 nm gaps were fabricated. For sub‐10 nm etched stru...