Record-low sheet-resistance of ∼128Ω/sq have been obtained in two-dimensional electron gases at ultrathin single AlN/GaN heterojunctions by optimizing the metal fluxes used in molecular beam epitaxy growth. Multiple 2DEGs have been found in AlN/GaN superlattices, with the net electron density measured >1×1014cm−2 at room temperature. This very high electron density also leads to a further lowering of sheet resistance to values far below what is achievable in single nitride heterojunctions. These low resistance channels are induced entirely by polarization in nominally undoped heterostructures, and are attractive for various device applications such as high speed transistors and intersubband detectors.