Joule heating measurements are carried out over a wide range of temperatures on a two-dimensional electron gas fabricated in an In 0.52Al 0.48As/In 0.53Ga 0.47As/In 0.52Al 0.48As heterostructure system that has a 25 nm wide In 0.53Ga 0.47As quantum well region. The energy loss rate is observed to be an indicator of the electron–phonon coupling processes in these systems. The temperature dependence of the energy loss rate is studied from 30 mK to 30 K and points toward a possible dominant unscreened piezoelectric coupling to the acoustic modes over temperatures of 1– 30 K , with boundary scattering in the ohmic contacts gaining importance at very low temperatures. The temperature decay of the energy relaxation time exhibits a T −3 behavior at high temperatures that transitions to a T −1 at lower temperatures and tends to saturation at millikelvin levels.