High-k ZrO2/Si films were fabricated by a sol-gel method and the effects of the thickness of ZrO2 on the phase formation, interface chemical structure, and dielectric performance were studied. The 0.1 M precursor sol was prepared by using Zr acetylacetonate, coated, dried on Si substrates, and finally annealed at 500 °C. The thickness of ZrO2 was varied in the range from 7 to 51 nm by repeating the coating and drying sequences. The deposited ZrO2 was amorphous for the sample with a thickness of ∼7 nm, but tetragonal (t-) phases appeared as the thickness increased. As the thickness increased, the flat-band voltage and hysteresis width in the capacitance-voltage curves increased. The sol–gel deposited ZrO2 dielectrics showed a high k value (∼33) due to the formation of the t-phase, while retaining gate leakage current levels of less than ∼4.0 × 10∼−5 A/cm2 at 1 MV/cm.