In order to make practical single-electron transistors (SET) that can operate at room temperature, it is necessary to determine the process factors that most influence their characteristics. For that purpose, the relationship between the oxidation temperature and the electrical characteristics of SETs was examined using SETs fabricated with precise dimensions by e-beam nanolithography, because a Si nanowire must be oxidized to convert it into the small Si island and tunnel barriers required for a SET. SETs fabricated using a relatively low oxidation temperature, such as 800degreesC, were found to exhibit clear Coulomb blockade oscillations at room temperature; while SETs fabricated using a temperature of 900 degreesC did not, even though the nanowires were about the same size. At intermediate temperatures, such as 850 degreesC, the characteristics were between those for 800 and 900 degreesC oxidation. The most probable explanation for these results is as follows: The small roughness inherent to the resist is transferred to the nanowire during etching and remains after oxidation, provided that the oxidation temperature is low enough. This results in the formation of, multiple islands, which can be extremely small and which enable the room-temperature operation of a Si SET due to the quantum-mechanical size effect. (C) 2003 American Vacuum Society.