[en] Si-on-insulator structures formed by implantation of oxygen (SIMOX) in a single step to a dose approx = 1.8 x 10¹⁸ O⁺ cm^-2 into p-type (0 0 1) Si and high temperature annealing have been studied by K-band electron spin resonance (ESR) at 4.3-31 K. γ-irradiation to a dose of 1 Mrad (Si) is found to introduce a new anisotropic ESR signal originating from a shallow donor in Si. It is tentatively assigned to an oxygen-related double donor intrinsic to SIMOX, which ionization state is tuned by changes in Si band bending resulting from modification of the net charge in adjacent SiO₂ by γ-irradiation. Possibly, this centre relates to the new donors recently suggested from transport measurements. (author)