A study of charge injection in metal‐ ‐silicon (MAOS) structures has been made using the capacitance‐voltage technique. Thin films were grown thermally on the Si substrates, whereas layers were obtained by pyrolytic deposition from in a NO‐forming gas mixture. Independent of the electrode material, negative charge is introduced into the oxide system when a positive voltage is applied to the metal. With Al electrodes, the oxide also becomes negatively charged under negative bias. Only for large negative voltages will a gradual loss of negative charge occur, leading to a net positive oxide charge. Charge injection under negative bias is not observed on O2 annealed layers, or on samples with Au electrodes. The results are discussed in terms of a qualitative model.