Flat-band potentials of n-GaN and selectively doped n-In0.17Ga0.83N/GaN quantum wells (QWs) grown by metalorganic vapor phase epitaxy are determined by measuring the bias dependence of photoluminescence intensity in electrolyte solutions for different pHs. The In0.17Ga0.83N/GaN QWs with the absorption edge of 430 nm in the photocurrent spectrum, has a lower flat-band potential (-0.86 V vs. Ag-AgCl) than that of n-GaN (-1.07V), but the flat-band potential of QWs is still higher than the hydrogen generation potential (approximately -0.6V) at pH 6.86. The difference in flat-band potentials observed between n-GaN and In0.17Ga0.83N/GaN QWs is smaller than the conduction band-offset estimated from the reported relationships by more than 0.1 V. (c) 2006 Elsevier B.V. All rights reserved.