Thermal heat management profoundly affects AlGaN/GaN high-electron-mobility transistors (HEMTs) overall performance and reliability. Understanding and improving the thermal performance of these devices depends on thermal resistance modeling. This work extensively reviews the methods and tools used for AlGaN/GaN HEMT thermal resistance modeling. Different fundamentals of thermal resistance modeling with their characteristics are also incorporated. The impact of the heat transfer mechanism in AlGaN/GaN HEMT is discussed in this review. We review the various simulation methods, material characteristics, and experimental procedures used to determine the various simulation methods, material characteristics, and testing approaches used in determining thermal resistance. We also investigate how various material characteristics, device designs, key parameters influencing thermal resistance, and packaging strategies affect thermal performance. The overview of steady-state and transient measurement techniques are analyzed to examine the thermal behavior of the AlGaN/GaN HEMT. Different analytical models are evaluated with their performance for accurate thermal resistance estimation. Numerical simulation techniques FEA, CFD, FDM, and Monte Carlo Method are briefly discussed with their geometry and boundary conditions. Material properties and their characterization for AlGaN/GaN HEMT thermal resistance modeling are observed. We have also reviewed different design strategies to mitigate the thermal resistance in AlGaN/GaN HEMT. A Unify packaging technique significantly improved heat dissipation and thermal resistance management. Advanced approaches and future trends of AlGaN/GaN HEMT with thermal resistance modeling are discussed at last. To enable the creation of improved and more reliable AlGaN/GaN HEMT devices, we summarize present challenges and potential future paths in thermal resistance modeling. To provide opportunities for researchers and engineers to improve their design and thermal management methodologies, an exhaustive investigation of the thermal behavior of AlGaN/GaN HEMTs is needed.