We fabricated gallium oxide (Ga2O3) Schottky barrier diodes using β-Ga2O3 single-crystal substrates produced by the floating-zone method. The crystal quality of the substrates was excellent; the X-ray diffraction rocking curve peak had a full width at half-maximum of 32 arcsec, and the etch pit density was less than 1×104 cm-2. The devices exhibited good characteristics, such as an ideality factor close to unity and a reasonably high reverse breakdown voltage of about 150 V. The Schottky barrier height of the Pt/β-Ga2O3 interface was estimated to be 1.3-1.5 eV.