We report a thorough study of the growth of self-assembled GaN/AlN quantum dots (QDs). These QDs were grown on sapphire substrates using the Stranski-Krastanov (SK) growth mode by means of low-pressure metal organic vapor phase epitaxy. The influence of the V/III ratio on the QD height, shape, and density is studied. Emissions above (3.8 eV) and below (2.8 eV) the band gap of GaN are observed for small dots (1.3 nm) and large ones (4.4 nm), respectively. Special emphasis was given to the SK growth mode transition and the parameters influencing the QD formation. The two-dimensional-three-dimensional transition is studied continuously by photoluminescence mapping showing its high sensitivity to the V/III ratio. (C) 2006 American Institute of Physics. (C) 2006 American Institute of Physics.