Abstract: In this work, the changes of irradiation defect in high dose neutron-irradiated Czochralski silicon (CZ–Si) at different annealing temperatures was investigated using the Positron annihilation spectroscopy (PAS) and Fourier transform infrared spectrometer (FTIR) technique. It is found that divacancy and abound in irradiated CZ-Si. With the increase of the annealing temperature the monovacancy type defect (such as VO) is annihilated. The results of PAS and FTIR show that the formation of is enhanced when the annealing temperature ran up to 400–600°C and with the FTIR absorption peak at the wave number of (VO) disappearing, five absorption peaks appear at the wave number of (), , , and . It can be concluded that these defect-impurity complexes prolong the lifetime of positrons. [Copyright &y& Elsevier]