The effect of the silicon top layer on the uptake and release of deuterium by silicon implanted with oxygen (SIMOX) was studied using thermal desorption measurements. The deuterium is incorporated in the buried oxide by disruption of the Si–O bridging bonds. The data reveal that the top layer reduces the uptake at 1073 K. Furthermore, it retards release; a moderate (≈1125 K) and a high-temperature (≈1400 K) retention were observed. It is proposed that release is accompanied by the reconstruction of the Si–O bonds and that the bare oxide surface constitutes an abundant source for defects thus enhancing the generation and elimination of Si–O bridging bond defects. ©1998 American Institute of Physics.