Surface photovoltage spectroscopy (SPV) is widely used for semiconductor characterization in modern microelectronics. Herein, the results of a comprehensive SPV analysis of oxidized n‐ and p‐type Czochralski (Cz) Si wafers with an oxygen concentration of about 5–7 × 1017 cm−3 are reported. It is demonstrated that the oxidation of the wafers with different H2/O2 ratios can significantly influence the diffusion length of minority carriers in p‐type Si. This effect is explained by the formation of oxygen–hydrogen‐related defects which are strong recombination centers in such wafers. In addition, a significant degradation of the diffusion length of minority carriers is observed in oxidized p‐type Si wafers after annealing at 90 °C and a subsequent illumination at room temperature. This degradation is found to be independent of oxide growth conditions, and it is not observed in n‐type wafers. This degradation is correlated with the presence of low concentrations of interstitial Fe (<1011 cm−3) in some wafers and with boron–oxygen‐related defects in some other wafers.