A novel fabrication technique involving the use of focused ion beam (FIB) selective implantation to fabricate nanostructures on crystalline Si substrates in conjunction with anisotropic etching is described. Using this maskless & resistless approach, Si nanostructures were fabricated by FIB implantation of Ga+ at doses from 1015 to 1016/cm 2. Wet etching in KOH/IPA does not attack the implanted region, while it removes the underlying Si anisotropically, with a very low etch rate on the {111} planes. The result is a cantilever-like structure whose thickness is dependent on the implantation energy and dose. Pre-etching rapid thermal annealing at 600°C for 30 sec does not prevent structure fabrication and post-etching RTA does not affect the shape of the structures.