Abstract Electron Paramagnetic Resonance measurements have been made on silicon-on-silicon dioxide and silicon-on-silicon nitride structures produced by ion implantation. In the former type of structure the EPR spectra have been ascribed to the oxygen vacancy centre E1” in the SiO2, the defect PMb0 at the Si/SiO2 interfaces and the amorphous silicon centre in the bulk silicon. A single line of width ΔB pp= 0.84(2) mT and an isotropic g = 2.0039(2) has been found in the latter structure and is attributed to silicon dangling bonds in the silicon nitride. The annealing behavior of these defects both in air and nitrogen has been measured.