In AlGaN/GaN heterostructure field-effect transistor structures, the surface defects and dislocations may serve as trapping centers and affect the device performance via leakage current and lowfrequency noise. In this paper we report results of our investigation of the trapping characteristics of SiO 2 -passivated Al 0 2 Ga 0 8 N/GaN heterostructure field-effect transistors using the capacitancevoltage (CV) profiling technique. From the measured frequency dependent CV data, we identified the characteristics of the traps at the AlGaN/GaN interface adjoining the channel and on the surface along the ungated region between the gate and drain. Based on the measured data, the influence of the channel traps on the low-frequency noise spectra and the effect of the surface traps on possible leakage noise are analyzed and compared with the previous studies.

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