The effect of high‐temperature treatments in inert atmosphere, performed after deposition of phosphorus‐doped polycrystalline silicon, on the accumulation of radiation‐induced charge in Si*SiO2Si structures is investigated. It is shown that these treatments lead to an increase of hole trap concentration on both SiO2 interfaces, and the hole trap creation at the Si*SiO2 interface is related with phosphorus diffusion from Si* into SiO2. A model of charge accumulation at the Si*SiO2 interface is proposed, which satisfactorily explains experimental data.