An all-silica Fabry-Perot interferometer (FPI) based on a microbubble for high-pressure and high-temperature measurements is proposed and demonstrated. The microbubble-based air cavity is fabricated using a hollow silica tube and a single-mode optical fiber for pressure sensing. The suitable thickness between the two end faces of the microbubble enables the silica cavity to be used for temperature sensing. The wavelength shift of the reflection spectrum versus pressure is linear, and the sensitivity reaches -5.083 nm/MPa at room temperature (20 °C) within the range of 0 - 4 MPa. The temperature sensitivity reaches 12.715 pm/°C within the range of 20 - 700 °C. The very low temperature-pressure cross-sensitivity of the two cavities indicates that the proposed FPI sensor offers great potential for simultaneous high-pressure and high-temperature measurements in harsh environments.