Ultra-thin Au films with thickness (h) ranging from 0.5 to 6.0 nm were deposited at room temperature (RT) by means of e-beam evaporation on SiO{sub 2} and HfO{sub 2}. Due to the natural solid-state dewetting (SSD) of the as-deposited films, Au nanoparticles (NPs) were formed on the substrates. By properly adjusting the h value, the size and the density of the Au NPs can be finely tuned. For h = 0.5 nm, spherical-like Au NPs with diameter below 5 nm and density in the order of 10{sup 12} Au NPs cm{sup −2} were obtained without any additional thermal treatment independently from the substrate. The dependence of the Au NPs characteristics on the substrate starts to be effective for h ≥ 1.0 nm where the Au NPs diameter is in the 5–10 nm range and the density is around 10{sup 11} Au NPs cm{sup −2}. The effect of a subsequent high temperature (400–800 °C) annealing in N{sub 2} atmosphere on the Au NPs was investigated as well. For h ≤ 1.0 nm, the Au NPs characteristics evidenced an excellent thermal stability. Whereas the thermal treatment affects the cristallinity of the Au NPs. For the thicker films (2.0 ≤ h ≤ 6.0 nm), the thermal treatment becomes effective to induce the SSD. The proposed methodology can be exploited for the synthesis of Au NPs with diameter below 10 nm on different substrates at RT. (paper)