We experimentally demonstrate high optical quality factor silica microdisk resonators on a silicon chip with large wedge angles by reactive ion etching. For 2-μm-thick microresonators, we have achieved wedge angles of 59°, 63°, 70°, and 79° with optical quality factors of 2.4 × 10⁷, 8.1 × 10⁶, 5.9 × 10⁶, and 7.4 × 10⁶, respectively, from ～80 μmdiameter microresonators in the 1550 nm wavelength band. Also, for 1-μm-thick microresonators, we have obtained an optical quality factor of 7.3 × 10⁶ with a wedge angle of 74°.