In this paper, we present ultra-high quality factor (<inline-formula> <tex-math notation="LaTeX">{Q} </tex-math></inline-formula>) SAW resonators fabricated on aluminum gallium nitride on gallium nitride on silicon (AlGaN/GaN/Si) heterostructures with <inline-formula> <tex-math notation="LaTeX">{Q} </tex-math></inline-formula> exceeding 6000 at room temperature. We characterize their temperature response in a broad range of temperature (−196°C to 500°C or 77 K to 773 K). The effect of doping on the <inline-formula> <tex-math notation="LaTeX">{Q} </tex-math></inline-formula> and temperature coefficient of frequency (TCF) of the GaN-based SAW resonators is analyzed, for the first time, using un-intentionally doped GaN (UID-GaN), carbon doped GaN (C-doped), and Si doped GaN. The <inline-formula> <tex-math notation="LaTeX">{Q} </tex-math></inline-formula> value for UID-GaN and C-doped GaN is similar and decreases from 2000 to 1000 as the temperature is increased from 77 K to 773 K. The <inline-formula> <tex-math notation="LaTeX">{Q} </tex-math></inline-formula> value of Si-doped GaN is higher than UID and C-doped GaN by a factor of 3 (6622 at 77 K) and decreases with increase of temperature. This value of <inline-formula> <tex-math notation="LaTeX">{Q} </tex-math></inline-formula> at 1.8 GHz is the highest reported amongst aluminum nitride (AlN) or GaN-based SAW resonators. For extreme high temperatures (≥573 K) the TCF value is half the TCF value of UID and C-doped GaN, which shows the possibility of engineering the TCF by tuning the doping concentration. For low temperatures (≤150 K) C-doped and UID-GaN show a turn over point in TCF curve which shows their promise for cold clocks. 2020-0163