The structure and activity of defects resulting from the etching reaction between Si adatoms and SiO 2 was probed by desorption of GeH x (x=1, 2, 3) dosed by hot-wire chemical vapor deposition. GeH x has been shown, in previous studies, to be inert to the SiO 2 surface and only accumulates through the formation of Ge clusters formed by reactions between adsorbed GeH x species. Temperature programmed desorption (TPD) of GeH x off SiO 2 surfaces subjected to varying degrees of etching reveals that the surface is activated toward GeH x resulting in the deposition of Ge. Examination of the H 2 signal during GeH x TPD, reveals two distinct peaks, one from 475K to 675K and another from 750K to 900K. The first H 2 peak is associated with the reaction of GeH x species with the hydrated form of the defect created by the Si etching reaction, while the second H 2 peak results from the reaction of GeH x species with Ge captured in the earlier reaction. Annealing a Si-etched SiO 2 surface under a diborane atmosphere deactivates the defect toward GeH x , while also deactivating intrinsic hydroxyl groups towards the adsorption of GeH x . A defect structure is proposed composed of vicinal and geminal hydroxyl groups flanking a Si vacancy.