A variety of applications from insulation to catalytic supports can benefit from lightweight, high surface area, mesoporous materials, which maintain their mesoporous structure to temperatures of 900–1200 °C. Silica aerogels begin to densify by 700 °C. Alumina aerogels are capable of higher temperature exposure than their silica counterparts, but undergo successive phase transformations to form transitional aluminas prior densifying to α-alumina. The present study characterizes the phase transitions of aluminosilicate aerogels derived from Boehmite powders to elucidate the role of time and temperature on phase transitions, surface area, and morphology. Aerogel compositions stable to 1200 °C for periods of 24 h have been demonstrated.