AlGaN/GaN and InAlN/GaN high electron mobility transistors (HEMTs) were fabricated and their electrical and thermal properties were examined. The influence of irradiation to direct current (DC) and low-frequency noise properties of these devices have already been investigated and published. However, the thermal processes in the active layers of these devices can also induce significant changes in the performance of devices. Since thermal processes are directly associated with temperature distribution, temperature mapping in the devices has been suggested using a mu;-Raman technique. Considering that the phonon frequencies are sensitive to the sample temperature, the shift of first-order Raman scattering can conveniently be used to directly measure the device temperature with a high spatial resolution. In this context, we report time resolved and sample mapping Raman spectra inside the HEMTs channel as measures of temperatures.