Room temperature characteristics of a single electron transistor fabricated using the AFM nano-oxidation process are described. A new and improved AFM nano-oxidation process is introduced, in which (1) the pulse-mode bias is used in-stead of DC bias, that can enhance the height and width aspect ratio of the oxidized metal and (2) atomically flat sub-strates such as α-Al₂O₃ are used instead of SiO₂ substrates. Using these new process, the single electron transistor was fabricated and it shows the clear Coulomb oscilation with the period of 1.8V and a Coulomb diamond characteristics even at higher temperatures than room temperature.