A simple concept of characteristic thermal length is used to develop a physics-based compact thermal circuit model for the multi-gate field effective transistor (MuGFET) structure including the device channel, fins, source/drain/poly pads, metal contacts, poly wire and metal mires. The characteristic thermal lengths are used to represent various heat loss paths of heat conduction along each segment of the fins, channels and poly/metal wires. Extraction of thermal resistances and thermal lengths used to construct the model is achieved through numerical simulations of the 2D cross section for each segment. The circuit models are developed for single-fin and multi-fin MuGFET structures, and simulations of the thermal circuits are performed in SPICE to validate the model for each structure.