For the first time, the time-dependent response of an AlGaN/GaN high electron mobility transistor (HEMT) pressure sensor is characterized at elevated temperatures. We show that temperature affects the sensitivity and the transient behavior of the sensor’s response to pressure. At a temperature above 125°C, the drain current response after the application of pressure transitions from exponentially decaying to exponentially growing. Using an Arrhenius model of trap activation energy, we demonstrate that two traps in the AlGaN/GaN heterostructure at 0.62 eV and 0.87 eV cause the temperature-dependent transient behavior. This work paves the way for creating reliable GaN-based sensing devices.