A novel empirical thermal modeling technique is proposed to allow improved prediction of channel temperature for GaN HEMT power devices when driven with pulsed DC/RF signals. The proposed thermal model contains a multiple-pole RC network and adapts itself based on the pulse width and duty cycles of the input signals. The model, which is incorporated within an Angelov-based compact non-linear model, is derived from numerical physics-based thermal analysis results. The model enables designers to conveniently estimate peak and average channel temperatures for specified pulse conditions and load and source impedances. The model can be used in either transient or in more time-efficient harmonic balance simulations.