The low frequency drain and gate noise-current characteristics of AlGaN/GaN heterostructure field effect transistors (HFETs) of two recently proposed isolation-feature topologies are experimentally investigated. In light of this study, suitability of high frequency operation of these technological alternatives is evaluated. These device types include "fin-isolated" (i.e., devices built on fins of size 16 mu m x 40 mu m), and "island-isolated" (i.e., devices built on an array of islands of size 16 mu m x 7 mu m). The low frequency noise characteristics of these devices are compared to the traditional "mesa-isolated" HFETs (i.e., devices built on conventional mesas of dimension 70 mu m x 100 mu m). Whereas generation-recombination (G-R) bulge signatures are absent from the low frequency noise spectra of the mesa- and fin-isolated devices, such features are observed on gate and drain noise-current spectra of island-isolated HFETs. Further exposure of the gate and ohmic electrodes to etched surfaces in island-isolated devices is deemed responsible for emergence of G-R signatures. (C) 2013 Elsevier Ltd. All rights reserved.