The growth of Ge quantum dots on various nitrided oxides has been achieved by ultra-high-vacuum chemical-vapor deposition with GeH4 gas at temperatures between 550 and 650 degreesC. The characteristics of the Ge dots were investigated using atomic-force microscopy, Auger electron spectroscopy, and x-ray photoelectron spectroscopy in order to find the mechanism of the Ge dot formation. On N2O-annealed nitrided oxide films, we obtained Ge dots with height and diameters of 3.2 and I I nm, respectively. No Ge dots were formed on surfaces of other dielectric substrates at 550 degreesC. From our experimental results, we suggest that the surface of N2O-annealed nitrided oxide contains a large amount of defects such as dangling bonds, which act as Ge nucleation sites. This is further confirmed by studying the growth kinetics and the influence of in situ annealing of the samples.