The effect of tetramethylammonium hydroxide (TMAH) treatment on the electrical properties of Ni/Au/GaN Schottky diodes have been investigated by current-voltage (I-V) and capacitance-voltage (C-V) techniques. The barrier heights and ideality factors measured from I-V characteristics are found to be 0.70 eV and 132 for without TMAH treatment, and 0.78 eV and 1.14 for with TMAH treatment, respectively. Cheung method is used to measure the series resistance and barrier height of the Schottky diodes, and the barrier height consistency is checked using the Norde method. The magnitude of interface state density for the diodes without and with TMAH treatment are varied from 7.45 x 1013 eV(-1) cm(-2) to 6.09 x 10(12) eV(-1) cm(-2) and 4.03 x 10(13) eV(-1) cm(-2) to 1.79 x 10(12) eV(-1) cm(-2) in the below the conduction band from E-C-0.19 eV to E-C-0.63 eV and E-C-0.22 eV to E-C-0.73 eV. Based on the results, the TMAH treatment effectively removes of surface oxide (GaxOy) layer, formed due to the incorporation of the residual oxygen with Ga atom at the GaN surface during the plasma etching. The decrease in interface state density at the Ni/Au/GaN interface could be the reason for the improvement in the electrical properties. (C) 2013 Elsevier B.V. All rights reserved.