Free-standing piezoelectric AlGaN/GaN beam resonators have been prepared on silicon substrates. The two-dimensional electron gas at the interface of the III/V heterostructure has been employed to act as back electrode for the piezoelectric active layer. The fundamental mode as well as higher order resonant modes of flexural vibration has been excited piezoelectrically and analyzed using optical laser–Doppler vibrometry. The experimental investigations were carried out under normal ambient conditions. The specific piezoelectric actuation scheme is described and the dependence of the measured resonant frequencies between 0.2 and 8.1 MHz on geometry and material parameters is investigated.