Measurements of the low-frequency noise between 1 Hz and 100 kHz in AlSb/InAsSb HEMTs are reported. At room temperature, over the lower part of the frequency range, the slope of the noise level is close to ideal 1/f. The corresponding Hooge parameter, alpha(H), was found to be 1.4 x 10(-3). In the high-frequency part of the spectrum, the start of a noise Lorentzian component is apparent. At lower temperatures, this component becomes fully visible and moves down in frequency with decreasing temperature, indicating the presence of a discrete trap level with an activation energy of 0.38 eV. Also at low temperatures, when the devices are illuminated with visible light, the noise increases greatly, displaying a prominent Lorentzian component with the characteristic 1/f(2) slope above the corner frequency. Published by Elsevier Ltd.