The effects of 1 nm thick CeO x capping on 7.5 nm thick Y-doped HfO2 films on the ferroelectric characteristics are investigated. From the ferroelectric characteristics of the samples annealed at different temperatures from 450 °C to 600 °C and annealing durations, the time (τ) required to stabilize the ferroelectric phase at each temperature was shortened by the capping. The identical activation energy (E a) of 2.65 eV for ferroelectric stabilization without and with capping suggests the same kinetics for phase transformation. However, an increase in the remnant polarization (P r) was obtained. Only a few Ce atoms diffused into the underlying HfO2 film even after 600 °C annealing. Ferroelectric switching tests revealed an improvement in endurance from 107 to 1010 by the capping, presumably owing to the suppression of conductive filament formation. Therefore, CeO x capping is effective in promoting the ferroelectric phase in HfO2 with high switching endurance.