A vertical‐type mesa‐gate GaN metal–oxide semiconductor field‐effect transistor (MOSFET) has been fabricated. The mesa‐gate structure can be easily achieved by a single deep etch to the n + ‐GaN which is the drain of the device, whereas the trench‐gate structure, the commonly used structure for the vertical‐type MOSFETs, requires an additional etching process to define the gate region. The mesa‐gate GaN MOSFET exhibited a normally‐off operation with the threshold voltage of 3 V, a normalised drain current of ∼ 55 mA/mm and a high on/off current ratio of 10 8 .