4.4 kV β-Ga₂O₃MESFETs with power figure of merit exceeding 100 MW cm^-2

β-Ga2O3 metal-semiconductor field-effect transistors are realized with superior reverse breakdown voltages (V BR) and ON currents (I DMAX). A sandwiched SiN x dielectric field plate design is utilized that prevents etching-related damage in the active region and a deep mesa-etching was used to reduce reverse leakage. The device with L GD = 34.5 μm exhibits an I DMAX of 56 mA mm-1, a high I ON/I OFF ratio >108 and a very low reverse leakage until catastrophic breakdown at ∼44.4 kV. A power figure of merit (PFOM) of 132 MW cm-2 was calculated for a V BR of ∼44.4 kV. The reported results are the first >4 kV class Ga2O3 transistors to surpass the theoretical unipolar FOM of silicon.