The bulk-quantity synthesis of single-crystal GaN nanowires has been achieved through a simple method of hot filament chemical vapor deposition without using a nanometer-sized catalyst. The microstructures and optical properties of GaN nanowires have been studied by electron microscopy and photoluminescence (PL) measurements at room temperature. The GaN nanowires had diameters of 5–12 nm and lengths of a few micrometers, and were highly pure. They possessed a hexagonal wurtzite structure and had a growth direction perpendicular to the {11̄01} plane. The PL spectra showed a broad emission peak centered at 420 nm.