In this paper, we present a normally-off GaN-based transistor with an extremely low on-resistance (R on ) fabricated by using a Ge-doped n ++ -GaN layer for ohmic contacts. We developed a novel GaN regrowth technique using Ge as a dopant, which achieved an extremely high doping concentration of 1 × 10 20 cm -3 , and thereby the lowest specific contact resistance of 1.5 × 10 -6 O 2 . The NiO gate fabricated using an atomic layer deposition technique reduced the spacing between the source and drain electrodes. The fabricated device showed the record-breaking Ron of 0.95 O&mm with the maximum drain current and transconductance of 1.1 A/mm and 490 mS/mm, respectively. Note that the obtained threshold voltage was 0.55 V. This extremely low Ron characteristic indicates the great potential of NiO-gate GaN-based heterojunction field-effect transistors.