In this study, GaN-based vertical FinFET device using HfO 2 as a high-κ dielectric gate layer to improve the breakdown voltage is designed. Simulation results show that a breakdown voltage as high as 2139 V can be achieved for the optimized GaN-based FinFET with a fin channel width of 200 nm, a channel doping concentration of 1 × 10 16 cm −3 , and a drift layer thickness of 10 μm. In addition, the proposed device has a low specific on-state resistance of 0.84 mΩ cm 2 , resulting in a large Baliga optimum figure of merit (FOM) 5.45 GW cm −2 . This work could lay a foundation to further improve the electrical performance of GaN-based vertical FinFET devices.