Through this work, a unique substrate temperature dependent evolution of hot electron distribution is reported in GaN HEMTs on C-doped GaN buffer, and its reliability consequences are discussed. With rise in substrate temperature, significant rise in hot electron concentration, its energy, and interaction with buffer traps is observed at the drain edge, in contrast to an expected reduction in hot electron population. A mechanism based on carrier de-trapping and transport to drain is proposed and experimentally validated.