Compared with its lateral counterpart, vertical GaN-on-GaN device can extend the voltage/power ratings and yield superior dynamic performance, showing potential for high-frequency and high-efficiency power electronics applications. This work presents the recent advances in structure design, fabrication and key mechanisms of vertical GaN diodes and transistors, primarily including the follows: (1) By utilizing the tunneling-enhancement layer with polarization effects in GaN, the trade-off between forward conduction and reverse blocking capability in unipolar GaN diode can be optimized. (2) With photon recycling/re-absorption in the direct-bandgap GaN, the desirable conductivity modulation at on-state and zero reverse recovery during turn-off transient can be simultaneously achieved in bipolar GaN PiN diode. (3) Vertical GaN diodes exhibit current-collapse-free performance and superior surge current ruggedness. Moreover, ultrafast junction temperature mapping has been developed to identify the failure mechanism during surge current transients. (4) By virtue of an AlN interfacial-layer to suppress the interface traps and carrier scattering, vertical GaN trench MOSFET featuring a high inversion channel mobility and high Baliga’s figure-of-merit has been achieved.