A process for fabricating thin Si nanowires is proposed which can reduce the parasitic series resistance of the nanowire. The process includes electron cyclotron resonance plasma deposition of a SiO2film through the openings of a patterned resist film. Since the SiO2thickness decreases as the opening narrows, the SiO2film can be made thinnest in the nanowire region. Therefore, during the following reactive‐ion etching, the SiO2film in this region is removed first and the Si layer is then selectively etched. A Si nanowire fabricated through this process shows quantized conductance at temperatures as high as 200 K.