We report the Metalorganic Chemical Vapor Deposition (MOCVD) growth, fabrication, and characterization of solar blind AlxGa1-xN/GaN-based avalanche photodiodes. The photocurrent voltage characteristics indicate a reproducible avalanche gain higher than 25 at a 72 V applied reverse bias. Under a 25 V reverse bias voltage, the 100 mu m diameter devices had a maximum quantum efficiency of 55% and a peak responsivity of 0.11 A/W at 254 nm, and a NEP of 1.89x10(-16) W/Hz(1/2).