A　major　obstacle　in　the　commercialization　of　GaN-on-Si　RF　HEMTs　lies　in　the　elevated　thermal　resistance　introduced　by　the　AlN/AlGaN　multi-layer　buffer,　employed　for　stress　management.　This　issue　adversely　impacts　device　performance　and　reliability.　In　this　study,　the　structure　function　method　was　utilized　to　precisely　determine　the　intrinsic　thermal　resistance　of　GaN-on-Si　materials.　Results　reveal　that　a　single-layer　AlN　buffer　demonstrates　a　significantly　enhanced　heat　dissipation　capability　compared　to　conventional　AlN/AlGaN　multi-layer　or　superlattice　buffer.　Additionally,　the　thermal　performance　of　device　under　operation　was　quantitatively　assessed　using　static-pulsed　I-V　measurements.　Through　theoretical　simulations,　the　influence　of　GaN　buffer　structures　on　heat　distribution　within　GaN-on-Si　RF　devices　was　explored,　indicating　that　optimizing　GaN　buffer　thickness　can　further　enhance　thermal　performance.　This　research　offers　a　thorough　understanding　of　the　relationship　between　material　structures　and　RF　device　thermal　behavior,　providing　crucial　insights　for　the　thermal　management　design　of　GaN-on-Si　RF　HEMTs.