We report a cross‐correlated investigation, performed by means of Raman scattering and infrared spectroscopy, of coupled LO phonon‐plasmon modes in bulk GaN. Using different samples with different (high) residual concentrations of free carriers, we find that the high‐energy Raman mode follows closely the plasma frequency resolved from the infrared data. On the opposite, the low‐frequency modes appears down shifted, with respect to the standard TO phonon frequency, by about 11 cm−1. Both findings agree satisfactorily with predictions of the linear response theory for undamped phonon‐plasmon modes and establish Raman scattering as a powerful and nondestructive tool to investigate the residual doping level of GaN up to about 1020 cm−3 .