We report a new low-cost top-down silicon nanowire fabrication technology requiring only conventional microfabrication processes including microlithography, oxidation, and wet anisotropic plane-dependent etching; high quality silicon nanowire arrays can be easily made in any conventional microfabrication facility without nanolithography or expensive equipment. Silicon nanowires with scalable lateral dimensions ranging from 200 nm down to 10-20 nm and lengths up to approximately 100 microm can be precisely formed with near-perfect monocrystalline cross sections, atomically smooth surfaces, and wafer-scale yields greater than 90% using a novel size reduction method where silicon nanowires can be controllably scaled to any dimension and doping concentration independent of large contacting regions from a continuous layer of crystalline silicon.