Nonsurface-treated zinc oxide (ZnO) Schottky diodes were fabricated on a Si substrate using one of two different seed layers, prepared by either the sol-gel or hydrothermal method. Then, ZnO film was grown on a seed layer by the hydrothermal method, and Au/ZnO Schottky diodes were fabricated to study the effects of different seed layers on the electric behavior. Observations show that the Schottky diodes grown on a hydrothermal seed layer exhibit very good rectifying behavior with a rectification ratio as large as 8000 at a bias voltage of ±2 V. In contrast, an ohmic behavior is observed in the Schottky diodes with sol-gel seed layer. Capacitance-voltage measurements demonstrate that the Schottky diodes grown on the hydrothermal seed layer have a Schottky barrier height of 0.77 eV as a result of Zn vacancies. However, a surface downward band bending is obtained in the ZnO grown on the sol-gel seed layer. The downward band bending renders a high carrier concentration on the ZnO surface, which is caused by the oxygen vacancies. Atomic ratio of Zn/O was investigated using Xray photoelectron spectroscopy and carrier transport mechanism was studied by current-voltage measurement.