GaN/InGaN heterostructures were grown by molecular beam epitaxy on sapphire (0001). The photoluminescence (PL) of InGaN/GaN quantum wells rapidly vanishes when the temperature increases from 10 to 100 K and is totally quenched above 150 K. This is the consequence of the high density of dislocations (10(9)-10(10) cm(-2)) inherent to nitride layers grown on sapphire. InGaN/GaN quantum dots (QDs) have been fabricated by takings advantage of the Stranski-Krastanov growth mode. In this case, the PL intensity is still intense at room temperature. This is due to the three-dimensional localization of carriers in the dots which hinders their migration towards non-radiative centers. The radiative efficiency of InGaN QDs was further improved using an AlGaN cladding layer. The PL integrated intensity reduces by less than one order of magnitude between 10 and 300 K. (C) 2000 Elsevier Science Ltd. All rights reserved.