Single crystal and polycrystalline silicon films have been patterned and etched with a novel high-selectivity process using self-assembled monolayer resists of octadecylsiloxanes (ODS). The highest resolution patterning of sub-10 nm features has been demonstrated by scanning force microscopy imaging of ODS layers patterned with a focused electron beam. An all-dry UV/ozone developer has been used to remove residual carbon from the electron beam exposed regions to improve etch selectivity. The positive tone pattern transfer process consisted of a short buffered hydrofluoric acid wet etch to remove the silicon native oxide followed by a high-selectivity, low ion energy etch using Cl-2 and BCl3 in an electron cyclotron resonance reactive ion etch. Features have been etched up to 90 nm deep into Si(100) wafers and minimum feature sizes obtained are similar to 25 nm. Poly-Si films on SiO2 insulator layers have been similarly patterned and have been used in a combined process with photolithographic definition of microbridges to form narrow conducting channels in the poly-Si.