We report GaN n++/p++ interband tunnel junctions with repeatable negative differential resistance and low resistance. Reverse and forward tunneling current densities were observed to increase as Si and Mg doping concentrations were increased. Hysteresis-free, bidirectional negative differential resistance was observed at room temperature from these junctions at a forward voltage similar to 1.6V. Thermionic PN junctions with GaN homojunction tunnel contact to the p-layer exhibited forward current density of 150 kA/cm(2) at 7.6V, with a low series device resistance of 1 x 10(-5) Omega cm(2). (C) 2016 AIP Publishing LLC.