The interface of zirconium oxide thin films on silicon is analyzed in detail for their potential applications in the microelectronics. The formation of an interfacial layer of ZrSi$sub$x/O$sub$y. with graded Zr concentration is observed by the x-ray photoelectron spectroscopy and secondary ion mass spectrometry analysis. The as-deposited ZrO$_2$/ZrSi$sub$x/O$sub$y//Si sample is thermally stable up to 880$^{circ}C$, but is less stable compared to the ZrO$_2$/SiO$_2$/Si samples. Post-deposition annealing in oxygen or ammonia improved the thermal stability of as-deposited ZrO$_2$/ZrSi$sub$x/O$sub$y/Si to 925$^{circ}C$, likely due to the oxidation/nitridation of the interface. The as-deposited film had an equivalent oxide thickness of∼13 nm with a dielectric constant of ∼21 and a leakage current of 3.2${ imes}$10e-3 A/$ extrm{cm}^2$ at 1.5V. Upon oxygen or ammonia annealing, the formation of SiO$sub$x/ and SiH$sub$x/N$sub$y/O$sub$z/ at the interface reduced the overall dielectric constants.