In the process of avalanche injection of electrons into silicon dioxide, besides electron trapping in the bulk of the oxide, there are slow and fast interface states generated. The slow states are donors and positively charged when empty. Together with positive charge in the interface states, they compensate the negative bulk charge to give the turn-around effect. The final C-V curve is due to a complex sum of different charge components. The slow states can be discharged when heated under +5 V or higher biases at 160 °C or above. The final charge state is only semipermanent. Fast interface states are also annealed in the process, and the anneal is enhanced by a positive bias. Bulk trapped electrons are minimally perturbed by the anneal. It is postulated that the slow states may communicate with silicon through the fast interface states in a thermally activated process. In order to study bulk electron trapping, avalanche injection should be carried out at elevated temperatures.