A novel highly anisotropic room-temperature process for silicon etching, using mixtures of SF6 and CHF3 gases is presented. The etch rate, selectivity, de bias voltage and anisotropy as a function of the reactive ion etching conditions (mixture composition, pressure and rf power) are discussed. Excellent anisotropy combined with clean, damage-free surfaces and etching uniformity and reproducibility have been achieved. It was thus possible to fabricate free standing silicon wires with diameter less than 50 nm and with aspect ratios up to 50:1. Optical emission spectroscopy, ex situ x-ray photoelectron spectroscopy and atomic force microscopy were employed as plasma gas phase and surface diagnostics.