Catalyst-free GaN wires with 100–200 nm diameters are grown on bare c-sapphire substrates by a metal-organic vapor phase epitaxy approach using both low V/III ratio and V-III precursor flows that favor a reaction-limited growth regime. The polarity control of the initial seeds allows obtaining pencil-shape wires with very sharp pyramids at their top (∼5 nm diameter). These defect-free nanowires evidence excellent structural and optical properties as shown by a sharp photoluminescence linewidth (1–3 meV at 5 K).