The potential of AlGaN/GaN heterostructures for novel sensor devices is discussed. The two-dimensional electron gas which is formed at the AlGaN/GaN interface due to the difference in the spontaneous polarisation of the two adjacent III-nitride layers is shown to respond very sensitively to changes in the electrostatic boundary conditions caused by the adsorption of ions, wetting by polar liquids, exposure to gases, or the piezoelectric polarisation due to mechanical strain. Possibilities to use III-nitride heterostructures in future biosensors or integrated sensor devices are also mentioned.