The exciton radiative lifetime in submonolayer (SML) InGaAs∕GaAs quantum dots (QDs) grown at 500°C was measured by using time-resolved photoluminescence from 10to260K. The radiative lifetime is around 90ps and is independent of temperature below 50K. The observed short radiative lifetime is a key reason for the high performance of SML QD devices and can be explained by the theory of Andreani et al. [Phys. Rev. B 60, 13276 (1999)] calculating the radiative lifetime of QDs formed at the interface fluctuations of a quantum well, as the SML QDs are 20–30nm in diameter and embedded within the lateral InGaAs QW.