An AlxGa1-xN/GaN-based metal-ferroelectric-semiconductor (MFS) structure is developed by depositing a Pb(Zr0.53Ti0.47)O3 film on a modulation-doped Al0.22Ga0.78N/GaN heterostructure. In high-frequency capacitance–voltage (C–V) measurements, the sheet density of the two-dimensional electron gas at the Al0.22Ga0.78N/GaN interface in the MFS structure decreases from 1.56×1013 cm-2 to 5.6×1012 cm-2 under the -10 V applied bias. A ferroelectric C–V window, 0.2 V in width, is observed near the -10 V bias, indicating that the AlxGa1-xN/GaN MFS structure can achieve memory performance without the reversal of the ferroelectric polarization. AlxGa1-xN/GaN heterostructures are promising semiconductor channel candidates for MFS field-effect transistors.