We investigated the carrier transportation of ultrathin CeO2 gate dielectrics with rapid thermal annealing (RTA). After annealing, the effective oxide thickness was decreased and the characteristics were significantly improved. Temperature dependence of gate leakage current was studied and Frenkel-Poole dominated the conduction mechanism for low RTA temperature. As the annealing temperature increases, Fowler-Nordheim tunneling became much more important and the CeO2/n-Si electron barrier height of 0.75 eV was extracted for future modeling and simulation. In addition, the energy band diagram of Al/CeO2/n-Si structure was established for the first time. (C) 2004 The Electrochemical Society.