For the commercial implementation of GaN-based high electron mobility transistor (HEMT) and GaN-based pseudomorphic HEMT (pHEMT), the temperature dependency of the two-dimensional electron gas (2DEG) is crucial. Herein, the temperature dependency of 2DEG for AlGaN/GaN HEMT and AlGaN/InGaN/GaN pHEMT has been analyzed theoretically and experimentally over the temperature range of ?40 °C to 150 °C. From the experimental and numerical data, a decreasing nature of 2DEG density is noticed for both the devices. The reduction rate in magnitude is higher for AlGaN/GaN HEMT compared to AlGaN/InGaN/GaN pHEMT. It is identified that the reduction of conduction band offset at higher temperatures is responsible for this decreasing nature. Incorporation of an extra 5 nm thick pseudomorphic layer of InGaN in AlGaN/InGaN/GaN pHEMT improves the 2DEG transport properties and enhances the overall transistor performance. Comparatively, the AlGaN/InGaN/GaN pHEMT is found to be exhibiting better 2DEG stability with temperature than AlGaN/GaN HEMT.