A focused ion-beam system was used for structuring of silicon by local desorption of hydrogen from the HF-passivated surface. The native oxide which was formed on the depassivated regions was used as an etch mask for KOH. The etch contrast for Ga and Si ions was studied as a function of ion energy and fluence. With a fluence on the order of 10(13) cm(2), a feature height of 15 nm was obtained. The method was applied to produce 160 nm wide CoSi2 wires on a Si/CoSi2 heterostructure.