Polycrystalline thin films of BaTiO3 with a resistivity of 10(3) Omega cm were fabricated on Ti-covered silicon substrates by a hydrothermal method at temperatures as low as 160 degrees C. The films were formed by submerging the substrates in a 0.5 M Ba(OH)(2) aqueous solution sealed inside an autoclave, heating to 160 degrees C with a saturated vapor pressure around 0.8 M Pa, and holding for various periods from 1 up to 24 h. The film thickness increased as the treatment prolonged within a certain period. The subsequent firing in air at 600 degrees C was found to raise the resistivity substantially. The structure and properties of the films were characterized by using x-ray diffraction, scanning electron microscopy, cross-sectional transmission microscopy, Auger electron spectroscopy, Rutherford backscattering spectroscopy, and spread resistance probing. The film growth mechanism involved in hydrothermal kinetics was discussed. Three ways for hydrothermally synthesizing thick BaTiO3 films have been recommended.