We show that trapped holes at the Si‐SiO2 interface account for all of the interface states generated by gate‐positive irradiation of metal‐oxide‐silicon structures. The field‐induced conversion of trapped holes to interface states is found to be the rate‐limiting step in interface state buildup. Interface‐state generation by hole trapping at the Si‐SiO2 interface also plays a role for gate‐negative irradiation. However, our experiments demonstrate an additional avenue for interface‐state formation under these conditions. Holes created in the SiO2 layer are swept to the Al‐SiO2 interface where they release positive ions. The transport of these ions to the Si‐SiO2 interface under gate‐positive field results in new interface states. Our data do not support models involving liberation of protons in the bulk of the SiO2 layer by hole transport through the oxide.