In this paper, a CMOS compatible silicon nanowire (Si NW) fabrication method on bulk silicon substrate is carried out using the self-limiting oxidation (SLO) to accurately control its size and cross-sectional shape. A predictive model for the 2-D SLO of Si NWs is presented. In this model, both the reduced reaction rate and diffusivity result in the oxidation rate degradation. The orientation dependence and the deformation of silicon core and oxide shell are further discussed here. The modeling results show good agreement with the experimental data within a wide range of oxidation temperatures, oxidation time, and various initial silicon core sizes. This model provides useful process design guidelines for Si nanostructures, especially in controlling the final diameter and cross-sectional shape of Si NWs from the top-down approach.