Phonon modal nonequilibrium is believed to widely exist around nanoscale hotspots, which can significantly affect the performance of nano-electronic and optoelectronic devices. However, such a phenomenon has not been explicitly observed in 3D device semiconductors at the nanoscale. Here, by employing a tip-enhanced Raman thermal measurement approach, substantial phonon nonequilibrium in gallium nitride near sub-10 nm laser-excited hotspots is directly revealed for the first time. As further evidence, quantitative agreements between measurements and accurate first-principles-based phonon Boltzmann transport equation calculations are obtained. The large nonequilibrium is attributed to the strong Fröhlich coupling of electrons with longitudinal optical phonons and the large acoustic-optical phonon frequency gap in gallium nitride, which is further demonstrated in other common III-V semiconductors. This work establishes a viable approach for understanding nanoscale nonequilibrium phonon transport and can potentially benefit the future modulation of hot carrier dynamics.