GaN Schottky rectifiers have been fabricated on free-standing substrates and on epi/substrate structures. Forward turn-on voltages were as low as 3 V at 25 degreesC. Reverse recovery was complete in <600 ns; with a characteristic time constant of 163 ns. The temperature coefficient For reverse breakdown voltage (V-B) was -2.5 +/- 0.6 V K-1 which is much lower than for lateral rectifiers reported previously, where values up to -30 VK-1 were achieved. Reverse currents increased with rectifying contact diameter and V-B decreased with increasing contact size, The best on-state resistance was 20.5 m Omega cm(-2) for diodes with V-B =450 V, producing a figure-of-merit (YB)(2)/R-ON of similar to 10 MW cm(-2).