In this investigation, diffuse x-ray scattering, Bragg line profile, and transmission electron microscopy have been employed for the study of point defects and their interaction with oxygen impurities in heavily boron-doped Czochralski Si wafers during various thermal treatments between 450 and 1050 °C for time intervals from 2 to 128 h. Bragg line profile data show that (1) materials tend to become more perfect during the initial stages of thermal annealing regardless of anneal temperatures and (2) the integral width and full width at half-maximum both exhibit minima after a thermal treatment at 450 °C for 32 h while the opposite behavior is observed for a thermal treatment at 1050 °C. The diffuse x-ray scattering data have shown that (1) the nature of the predominant defects depends upon annealing temperature, time and ramping cycles; and (2) the mean cluster size ranges between 1.4 and 2.0×10 3 nm regardless of annealing temperature and time. Transmission electron microscopy results show (1) slower precipitation kinetics occur than in lightly doped materials, (2) virtually no precipitates have been observed, even after 128 h for annealing temperatures up to 650 °C, (3) amorphous precipitates with a {100} platelet morphology are observed after prolonged anneals at 800 °C, and (4) the appearance of complex precipitate structures have been observed at 1050 °C. These results indicate significantly different behavior from that of lightly doped silicon. Finally, using a thermodynamic and kinetic model, we attempt to explain these heavy boron doping effects on SiO2 precipitation in Czochralski Si.