Low-frequency noise in the frequency region of 20 Hz to 20 kHz is investigated in AlGaN/GaN high electron mobility transistors (HEMTs) grown on SiC substrates. The noise spectra have the form of the 1/f (flicker) noise. The measured Hooge parameter is as low as 0.0001. This value is comparable with Hooge parameter values for commercial GaAs field effect transistors and approximately two orders of magnitude smaller than Hooge parameter value measured for AlGaN/GaN heterostructures grown on sapphire. The level of noise depends on the gate leakage current; the noise is much higher in devices with a high gate leakage current. The small measured values of the Hooge parameter are related to a smaller leakage current and to a better material quality of the devices on SiC substrates and to a high electron sheet density. The low levels of the 1/f noise in the AlGaN/GaN HEMTs on SiC substrates make them suitable for applications in communication systems. © 1998 American Institute of Physics.