We explore the hydrogen-related microstructures involved in,hot electron defect creation at the Si(100)-SiO2 interface of metal-oxide semiconductor: held effect transistors. With ab initio density functional calculations, the energetics and defect levels have been calculated for hydrogen in bulk silicon, bulk silicon dioxide and at their, interface. We relate these calculations to several experiments and suggest a microscopic model for hydrogen-related hot electron degradation. (C) 2000 Academic Press.