The built-in potential phi(tot) of an isolated and of three stacked lens-shaped c-plane In0.2Ga0.8N/GaN quantum dots (QDs) is calculated using a surface integral approach. There remains disagreement about the sign of the shear strain piezoelectric coefficient e(15), with more recent analysis suggesting e(15) < 0. We show that with e(15) < 0, the potential phi(tot) changes sign outside an isolated QD, in contrast to the case with e(15) > 0. This behaviour affects phi(tot) in a system of stacked QDs. For small barrier thicknesses between the QDs, the potential in the central QD is strongly reduced compared to an isolated QD, independent of the sign of e(15). Using e(15) < 0 and small barrier thicknesses, the potential in the remaining two QDs is also slightly reduced, while for larger barrier thicknesses almost no reduction is observed. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim