p-i-n rectifiers were fabricated on epitaxial layers grown on free-standing GaN substrates. The forward turn-on voltage, VF was ∼5 V at 300 K and displayed a positive temperature coefficient. The specific on-state resistance (RON) was ∼5 mΩ cm2 at 300 K, with an ideality factor of ∼2 and activation energy for low forward current density of ∼1.6 eV. This is consistent with carrier recombination in the space charge region via a midgap deep level. The figure-of-merit, VB2/RON, where VB is the reverse breakdown voltage, was 0.32 MW cm-2. The reverse recovery time was ≤600 ns at 300 K. The improved forward characteristics relative to previous heteroepitaxial p-i-n GaN rectifiers show the advantages of employing a GaN substrate to make a true vertical transport geometry device. © 2003 American Institute of Physics.