Edge-terminated Schottky rectifiers fabricated on quasibulk GaN substrates showed a strong dependence of reverse breakdown voltage VB on contact dimension and on rectifier geometry (lateral versus vertical). For small diameter (75 μm) Schottky contacts, VB measured in the vertical geometry was ∼700 V, with an on-state resistance (RON) of 3 mΩcm2, producing a figure-of-merit V2B/RON of 162.8 MW cm-2. Measured in the lateral geometry, these same rectifiers had VB of ∼250 V, RON of 1.7 mΩcm2 and figure-of-merit 36.5 MW cm-2. The forward turn-on voltage (VF) was ∼1.8 V (defined at a current density of 100 A cm-2), producing VB/VF ratios of 139-389. In very large diameter (∼5 mm) rectifiers, VB dropped to ∼6 V, but forward currents up to 500 mA were obtained in dc measurements.