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 {<1(1)over bar 01>} plane. The PL spectra showed a broad emission peak centered at 420 nm.