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