To fabricate a metal oxide semiconductor field-effect transistor (MOSFET) with a three-dimensional (3D) structure, several problems arise in the conventional thermal oxidation (TO) process, such as leakage current, shape nonuniformity, stress concentration, and the dependence of the oxidation rate on the lattice plane of Si. To overcome these problems, we propose low-temperature (<300 °C) neutral beam oxidation (NBO) as an alternative oxidation process. We found that an oxide film grown by NBO (NBO film) exhibits performance characteristics of a gate dielectric film that are as high as those of thermal oxide films in terms of the relationship between equivalent oxide thickness (EOT) and leakage current. The rate of NBO is also independent of the lattice plane of Si, while the oxidation is beam orientation dependent. Therefore, growing oxide films by NBO is advantageous, in that the method can be applied to gate dielectric films for the 3D fin structure of field-effect transistors (FinFETs) and surrounding gate transistors (SGTs).