Raman spectroscopy measurements have been performed on GaAs:Be samples with high crystalline quality and exceptional heavy doping level ranging from 1019to 1.4×1021cm−3. The recorded spectra show a structure we assigned to a coupled LO phonon‐damped plasmon mode. A theoretical expression for the Raman scattering rate by this mode has been derived from a dielectric model and compared to the experimental data. Using a fitting procedure the doping level of the samples has been estimated in agreement with Hall measurements. Moreover, the study of the Raman intensity evolution of both unscreened‐LO and coupled phonon‐plasmon structures, provided a convenient and rapid method to determine the activated carrier density inp‐doped polar semiconductors. Disorder effects due to the dopant impurities have been also observed and analyzed using a spatial correlation model description.