Wide bandgap semiconductors (WBGS) can operate at high powers and frequencies, revolutionizing power electronics. However, as their power density continues to increase, thermal management issues become more prominent, which can limit further performance improvements. Accurate characterization and a thorough understanding of the thermal transport properties of WBGS are crucial for solving these challenges and optimizing heat dissipation. This chapter focuses on the thermal transport properties of the two most important WBGS: GaN and SiC. We discuss the influence of intrinsic factors, including anharmonic phonon interactions, phonon dispersion topology, and phonon-focusing effect on their thermal conductivity. Additionally, we review the roles of extrinsic factors, such as point defects (vacancies, impurities, alloying, isotopes, and free carriers), line defects (dislocations), and planar defects (grain boundaries and stacking faults). The effect of nanostructures and (quasi-) ballistic transport in GaN and SiC are also briefly discussed. Furthermore, we review the well-established thermoreflectance-based measurement techniques as powerful tools for characterizing thermal transport in GaN and SiC, including their principles, implementations, and applications to provide valuable insights into the thermal properties of GaN and SiC. Finally, a summary of challenges and opportunities in the thermal management of GaN and SiC-based electronics is presented.