The dispersion effects of transconductance (g/sub m/) and output resistance (R/sub ds/) in AlGaN/GaN MODFETs were investigated. The dispersion effects of g/sub m/ were found to be much smaller than those of R/sub ds/. Devices under different biases show g/sub m/ dispersion of /spl sim/ 4% to 7%, while R/sub ds/ dispersion of /spl sim/ 19 % to 44% in a frequency range of 50 Hz to 100 kHz. The trapping-detrapping time constants of the dispersion effects were extracted by employing a novel distributed RC network and carrier injection current sources. The time constants estimated are in a range of /spl sim/ 1.5 /spl mu/s to 1 ms.