GaN(Si)/AlInN multiple quantum wells were grown on GaN/Al2O3 (0001) templates by metalorganic vapor-phase epitaxy. Transmission electron microscopy observations showed well-defined GaN quantum wells and AlInN barrier layers. Electrostatic potential profiles across the heterostructure have been measured using off-axis electron holography. A polarization-induced electric field with magnitude of similar to 2.2 +/- 0.1 MV/cm was measured across the GaN quantum wells, in reasonable agreement with simulated values. However, the measured fields across the AlInN barriers were considerably less than predicted from simulations: possible reasons are briefly discussed. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4772633]