The register file is one of the hottest devices in processor- based systems. Leakage reduction techniques and DTM mechanisms re- quire a thermal characterization of the hardware. This paper presents a thermal model to analyze the temperature evolution in the shared reg- ister files found on VLIW systems. The use of this model allows the analysis of several factors that have an strong impact on the heat trans- fer. The results obtained can be used in the design of temperature-aware compilers and place&route tools.