High-quality pseudo-vertical p-n diodes using a GaN-on-silicon heterostructure are reported. An optimized fabrication process including a beveled deep mesa as edge termination and reduced ohmic contact resistances enabled high on-state current density and low onresistance. A uniform breakdown voltage was observed at 830 V. The positive temperature dependence of the breakdown voltage clearly indicates the avalanche capability, reflecting both the high material and processing quality of the vertical p-n diodes. The Baliga figure of merit, around 2 GW/cm², which is favorably comparable to the state-of-the-art, combined with avalanche capability paves the way for fully vertical GaN-on-Silicon power devices.