The pre-passivation surface treatment process with tetramethylammonium hydroxide (TMAH)-based wet solution was proposed for the minimization of the leakage current (I-leak) in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs). This process step contributes to the simultaneous decrease of the surface current (I-surf) in the active region of device and mesaisolated region by removing the surface states and traps related to nitrogen (N) vacancy, Ga-oxide, and dangling bonds. Using the surface treatment, the fabricated device achieves a lower off-state current (I-off) of similar to 10(-12) A/mm, a higher on/off current ratio (I-on/I-off) of similar to 10(11), a small subthreshold swing (SS) of 68.4 mV/dec. The reduced I-leak also improves breakdown voltage (BV). In addition, the interface trap density (D-it) between the SiN layer and the AlGaN surface was extracted to evaluate the quality of the SiN/GaN interface, which showed that the treatment decreases the D-it with reduction of the surface defects. (C) 2016 Elsevier Ltd. All rights reserved.