The evolution of the electron acoustic signal has been measured for Be‐ and Si‐doped GaAs and Ga0.28Al0.19In0.53As layers with doping levels from1017to 1020at. cm−3. The samples have also been analyzed by cathodoluminescence spectroscopy for near‐band‐edge transition and deep level emission. The results are explained by the reduction of the mean free path of phonons, giving rise to a lattice thermal conductivity decrease. Meanwhile, the electronic part of the thermal conductivity of these compounds is found to be nearly negligible.