ZrO2/Si thin films were fabricated using a sol-gel technique, and the chemical state change and structural evolution from sol to gel to Zr oxide by heat treatment were investigated. The precursor sol was synthesized using a Zr-acetylacetonate (Zr-acac) precursor, spin-coated, dried on Si(100) substrates, and then annealed at 300-700 A degrees C in air. With increased annealing temperature of the sol-gel-derived layer, Zr-acac decomposed into Zr-acetate, an amorphous ZrO2 phase formed, and crystallization into a tetragonal phase occurred. In addition, the ZrO2 layer became denser and the interfacial layer between ZrO2 and Si thickened, whereas the surface morphology was nearly unaffected and remained smooth with root-mean-square values < 4.5 .