The electronic band structure of a modulation-doped AlGaNAlNGaN superlattice structure where the AlGaN layer is compositionally graded has been experimentally determined by electron holography. It is shown that all periods in the superlattice have a similar two-dimensional-electron-gas distribution, indicating no degradation in the quality of the heterostructures during growth. High-resolution potential energy profiles show that the nominally linear grading of the AlGaN barrier layers results in a parabolic profile in Al composition. Knowledge of the nature of energy barriers for electron transfer between channels is important in the optimization of the perpendicular conductivity of AlGaNGaN superlattice structures. © 2007 American Institute of Physics.