We have investigated the electron energy relaxation of two-dimensional electron gas (2DEG) in AlGaAs/GaAs high electron mobility transistor (HEMT) channel at lattice temperature of T-L = 1.7 K under zero magnetic field. The electron temperature of 2DEG has been determined by using the absolute power dissipation in HEMT channel in the temperature range of 1.7-60 K. The experimental results are compared with theoretical results which include both acoustic phonon via deformation coupling and polar optic phonon scattering mechanisms. A good agreement is obtained between experimental and theoretical results for all electron temperatures. A transition between acoustic phonon and polar optic phonon regime has been seen at the electron temperature T-e = 40 K. The results are consistent with other studies where different techniques but similar sample structures have been used. The results also provide useful information about the relative magnitude of acoustic phonon via deformation potential coupling and polar optic phonon contributions to power loss of 2DEG. (C) 2003 Elsevier B.V. All rights reserved.