We have developed a very controllable fabrication process of an extremely narrow (∼10 nm) quantum wire metal‐oxide‐semiconductor field‐effect transistor (MOSFET) on a separation‐by‐implanted‐oxygen (SIMOX) substrate using anisotropic etching and selective oxidation technique. The drain current versus gate voltage characteristics show oscillations caused by Coulomb blockade even at room temperature. The oscillations split into several sharp peaks when the temperature is decreased, indicating that the channel is separated by several serial coupled quantum dots and that the quantum levels of these dots correspond to the observed fine peaks. ©1996 American Institute of Physics.