The objective of this application note is to provide users of Cree wide bandgap devices with a guideline of the thermal performance of high power SiC MESFET and GaN HEMT transistors. It explains the methodology that Cree uses to determine the thermal resistance values listed in its datasheets. As with all semiconductor devices SiC MESFET and GaN HEMT device reliabilities are dependent directly on maximum operating channel temperature. It is therefore important to determine, with a high degree of confidence, what the maximum channel temperature is under specific operating modes, particularly for products operating under CW and dissipating large amounts of thermal energy.