The use of (Ba0.5Sr0.5)TiO3 (BST) as the control oxide in a Au-nanocrystal-based memory structure was investigated. The Au nanocrystals, surrounded with a core shell of Au-doped BST, were self-assembled in a BST/SiO2 stack. The leakage of the gate dielectric is reduced by a partial dissolution of Au into the BST matrix, which enlarges the energy band gap of BST. Moreover, direct tunneling through the tunnel oxide is suppressed because the internal field induced by the charges in the Au nanocrystals can be screened by the ultrahigh-k shell of BST. Therefore, the retention property of the Au-nanocrystal-based memory structure is improved.