AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) with gate insulators grown using the photoelectrochemical oxidation method were fabricated in this work. The pinch-off voltage, maximum extrinsic transconductance, and drain-source saturation current at V-GS = 0 V were -9 V, 88.20 mS/mm, and 665 mA/mm, respectively. When the MOS-HEMTs operated at V-GS = -20 and 20 V, the gate leakage current was only 31 and 960 nA, respectively. The normalized noise power spectra of MOS-HEMTs operated in the linear region and the saturation region were fitted well by 1/f(gamma) law from 4 Hz to 10 kHz. The exponent gamma values were all closed to unity and independent of V-GS. In the linear region (V-DS = 2 V) at V-GS = -8 V and V-GS = 2 V, the alpha(ch) and alpha(s) estimated at a frequency of 100 Hz were 8.69x10(-6) and 9.29x10(-5), respectively. The alpha(ch) and alpha(s) estimated in the saturation region (V-DS = 10 V) at V-GS = -8 V and V-GS = 2 V at a frequency of 100 Hz were 1.61x10(-4) and 2.08x10(-3), respectively. The normalized noise power density was a function of V-G(-1), V-G(-3), and V-G(0) corresponded to the three regions of V-G <= 3 V (V-GS <= -6 V), 3 V <= V-G <= 9 V (-6 V <= V-GS <= 0 V), and V-G >= 9 V (V-GS >= 0 V), respectively, where V-G was the effective gate bias defined as (V-GS-V-off). (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3424900] All rights reserved.