In this paper, we present the results of photovoltage (PV), continuous wave (cw) and time-resolved photoluminescence (PL) measurements on a set of InGaN/GaN quantum wells (QWs) grown by metalorganic chemical vapor deposition on sapphire substrates. The energy difference between the absorption edge and PL peak increases with well width. The cw PL spectra exhibit blueshift with increasing excitation intensity and the blueshift drastically increases with the well width. The PL decay times in wider QWs are significantly longer than in narrower QWs. The PL decay times also decreases with increasing excitation intensity. It is found that the lattice-mismatch strain-induced piezoelectric field plays a important role in the optical transitions in InGaN/GaN QWs. circle dot 2004 Elsevier B.V. All rights reserved.