A series of high dielectric material Er₂O₃ thin films with different thicknesses were deposited on p-type Si (100) substrate by pulse laser deposition at different temperatures. Phase structures of the films were determined by means of X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). Leakage current density was measured with an HP4142B semiconductor parameter analyzer. The XRD and HRTEM results reveal that Er₂O₃ thin films deposited below 400 °C are amorphous, while films deposited from 400 to 840 ° are well crystallized with (111)-preferential crystallographic orientation. I-V curves show that, for ultrathin crystalline Er₂O₃ films, the leakage current density increases by almost one order of magnitude from 6.20 × 10⁻⁵ to 6.56 × 10⁻⁴ A/cm², when the film thickness decreases by only 1.9 nm from 5.7 to 3.8 nm. However the leakage current density of ultrathin amorphous Er₂O₃ films with a thickness of 3.8 nm is only 1.73 × 10⁻⁵ A/cm². Finally, analysis of leakage current density showed that leakage of ultrathin Er₂O₃ films at high field is mainly caused by Fowler–Nordheim tunneling, and the large leakage of ultrathin crystalline Er₂O₃ films could arise from impurity defects at the grain boundary.