The possibility of CeO2 thin films as insulators of metal ferroelectric insulator semiconductor (MFIS) structures was investigated. The (111)oriented CeO2 thin films were fabricated on Si(100) substrates using r.f. magnetron sputtering. High frequency capacitance-voltage (C-V) characteristics of the CeO2/Si structure fabricated at different deposition and oxygen annealing temperatures were analyzed. Interface trap densities were calculated using C-V data. The interface trap density increased as the deposition temperature increased, which may be due to the increase of the stress in the CeO2 film with the deposition temperature. Oxygen annealing at 500 degrees C is recommended to improve the high-frequency C-V characteristics of the CeO2/Si structure. The interface trap density was 6.8 x 10(10) eV(-1) cm(-2) after O-2 annealing at 500 degrees C, which was comparable to that of SiO2 thin films (5.6 x 10(10) eV(-1) cm(-2)).