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IR thermal image eve thermal energy [2]. The relatively poor thermal conductivity of GaN makes the thermal management of GaN power devices difficult. Junction temperaturesmustbecontrolledeffectively toguarantee the performance and reliability of components. Many RF transistor package designs use lead-frame and plastic overmolding and have temperature maps of device structures and packages during opera-tion. However, Joule heating in an AlGaN/GaN HEMT occurs within 0.5 mmof the drain side of the gate contact, and cannot bemeasured by IR thermography [8]. One potential consequence is underestima-tion of the real operating temperature of the device because of the diffraction limit of infrared light [9]. An accurate method for measuring device temperatures is critical to determining the effects of localized self-heating. Micro-Raman spectroscopy with a spatial resolution of 0.5e0.7 mm has been used to obtain temperature line * Corresponding author. Contents lists available at International Journal w.