The etching of silicon atom from the Si(1 0 0)-p(2 × 2) surface, i.e. the desorption of SiO molecules from this surface, either clean or pre-oxidized, is investigated at the density functional theory level. The reaction paths for desorption are given as a function of the initial oxidation state of the extracted silicon atom. The associated activation energies and the atomic configurations are discussed. Particularly, it is shown that desorption of SiO molecules takes place during conventional thermal oxide growth (∼2 eV activation) via non-oxidized silicon atoms. Further SiO extraction mechanisms of higher silicon oxidation states required higher temperatures. In particular, doubly oxidized silicon atoms (Si2+) are able to decompose with an activation of ∼4 eV which corresponds to the actual temperature where decomposition of oxides is observed. This confirms the statement that decomposition of oxide layer nucleates at the interface with silicon where Si2+ has been detected thanks to XPS experiment.