The improvement of the Schottky contact resistance in an AlGaN/GaN Schottky barrier diode was investigated using dense nanoscale mesa holes. The 100 nm mesa hole array under the Schottky metal added a Schottky contact to the mesa edge with a length of 9.4 µm/µm2. This decreased the contact resistance from 8.23 to 2.55 Ω·mm for a 15 × 100 µm2 AlGaN/GaN Schottky contact. Also, the transfer length of 12.5 µm was reduced to 3.6 µm by using the mesa array. The nanoscale mesa holes increased the Schottky current and enabled a narrow Schottky contact with high current density. The diode with a 2 × 100 µm2 Schottky contact that has mesa holes showed a current of 131 A/mm2 at 3 V, which is 3.1 times higher than that of a conventional structure.