The mechanism and characteristics of bias annealing of Fowler-Nordheim stress-induced leakage currents [SILC) in thin silicon dioxide films (4.5 nm) at room temperature have been investigated. It is shown that the degree of SILC reduction increases with the anneal gate bias, irrespective of the polarity of the anneal bias. Furthermore, the bias annealing of SILC is found to be greatly enhanced in a hydrogen ambient, thus providing a strong physical evidence that trapped holes are contributing significantly to SILC. The result also suggests that the mechanism uf bias annealing is: like ly related to the annealing of trapped holes. In addition, unbiased thermal annealing of SILC has been studied and compared to the bias annealing. A portion of the SILC apparently annealed out by bias annealing can be reactivated, while thermal annealing causes a permanent annihilation of SILC.