Combining SiGe/Si heteroepitaxy, selective chemical etching, and subsequent thermal oxidation, we have successfully fabricated ultrafine silicon quantum wires (SQWRs) with Si/SiO2 interfaces. Experimental result shows that the present method provides a very controllable way to fabricate ultrafine SQWRs, that is completely compatible with silicon microelectronic technology. As one of the key processes of controlling the lateral dimensions of SQWRs, wet oxidation of silicon wires have been investigated. It is found that a self-limiting oxidation phenomenon of silicon wires occurs for wet oxidation. This oxidation retardation characteristic of silicon wires is discussed.