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The junctions formed between gate contact and III-nitride are crucial components of GaN-based electronics and optoelectronics. In this work, solution-processed inorganic Ti3C2Tx MXene films were spray coated on the AlGaN/GaN epitaxial wafer as the gate contact. The workfounction of MXene films was effectively enhanced by partial oxidization process, and accordingly, the gate leakage current and off-state drain current were significantly suppressed. The van der Waals heterojunction between MXene films and III-nitride without direct chemical bonding retained the pristine atomically flat native oxides of III-nitride, record high Ion/Ioff current ratio of 1013, and near ideal subthreshold swing of 61 mV/dec was achieved in the Schottky-Type gate GaN HEMTs. In addition, the MXene gate GaN HEMTs display superior electron mobility and transcoductance, high uniformity with 20 measured transistors. The unprecedented performance can be correlated to the damage-free interface between MXene and III-nitride, negligible atomic diffusion of MXene into the semiconductor layer, and excellent adhesion between MXene and III-nitride. This work provides an alternative method to create contact not only in GaN HEMTs but also in other electronic and optoelectronic devices which uniquely features cost-effective, non-vacuum, high deposition rate, and damage-free properties.