The effects of high-temperature annealing on physical and electrical defects are investigated for a silicon-on-insulator (SOI) layer formed by separation by implanted oxygen (SIMOX). After oxygen implantation, the SIMOX SOI wafers were annealed at different temperatures in an Ar + 0.5% O-2 ambient. The oxygen precipitations in the SOI layer were completely dissolved at 1310 degrees C. Three electrical deep levels at 0.33 eV (D1), 0.40 eV (D2), and 0.48eV (D3) from the conduction bandedge were observed, regard less of annealing temperature. The concentrations of D1 and D2 were inversely proportional to the size of the oxygen precipitations. When the SOI layer, which was subjected to annealing at 1310 degrees C, was subsequently annealed at 1000 degrees C in an O-2 ambient, D1 and D2 disappeared, while D3 was unaffected. The sources of these deep levels were identified as small dislocation loops for D1, vacancies for D2, and threading dislocations for D3.