This work presents an experimental investigation and relevant discussion of the link existing between noise parameters and light exposure of GaAs pseudomorphic HEMT's at microwave frequencies. A 100 pm gate width AlGaAs/InGaAs/GaAs heterostructure device has been illuminated with CW visible laser light (650 nm) and a systematic analysis has been performed by examining the device behavior under controlled bias current conditions. Significant effects have been brought to evidence in the 2-26 GHz noise parameters F-min, Gamma(opt) and R-n measured in the different conditions. A clear correlation has been found between the level of degradation of the noise parameter behavior and the light exposure. (C) 2014 Elsevier Ltd. All rights reserved.