We report systematic characterizations of flicker noise in GaN based MODFETs. Flicker noise was measured across the channel of the devices from room temperature to 130 K. The voltage noise power spectra, SV
(f) were found to be proportional to 1/f
γ, where γ depends on the device temperature as well as the gate bias. Study of SV
(f) as a function of the biasing condition was conducted in detail and was found to vary as V
where β changes with temperature from about 2.1 at room temperature to about 0.9 at 130K. Analyses of the data showed that the noise originated from thermal activation of carriers to localized states in the channel area. The data suggested that the trapping and detrapping of carriers did not lead to fluctuations in the carrier concentration as postulated in the McWhorter’s model. However, more work is needed to determine if surface mobility fluctuations played key role in the 1/f noise.