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GaN quantum dots were grown on an Al(0.11)Ga(0.89)N buffer layer by using flow rate modulation epitaxy. The Stranski-Krastanov growth mode was identified by an atomic force microscopy study. The thickness of the wetting layer is about 7.2 monolayers. The temperature dependent photoluminescence studies showed that at low temperature the localization energy, which accounts for de-trapping of excitons, decreases with the reducing dot size. The decrease in emission efficiency at high temperature is attributed to the activation of carriers from the GaN dot to the nitrogen vacancy (V(N)) state of the Al(0.11)Ga(0.89)N barrier layer. The activation energy decreases with reducing dot size.