A strong piezoelectric effect and a large spontaneous polarization allow one to incorporate a large electric field (≫106 V/cm) and high sheet charge (≫1013 cm-2) without doping in the AlGaN/GaN heterostructure. Theoretical studies are done to examine how polarization effects can be exploited to design metal–AlGaN/GaN tunnel junctions. We find that with a proper choice of AlGaN thickness undoped junctions can be made with very high metal to two-dimensional electron gas tunneling. Thus, a Schottky junction can be converted to a tunnel junction without doping. The tunneling probabilities approach those produced in a system doped at ∼4×1019 cm-3. This work suggests that very interesting tunnel junctions can be made from undoped AlGaN/GaN heterostructures. © 2000 American Institute of Physics.