In this research, we applied several new ideas for a novel thermal convection inclinometer design. (1) A flexible polyimide (PI) substrate was used instead of a silicon wafer so that the new design can reduce the energy loss of the heater to the substrate. (2) Both the heater and thermal sensors were formed directly on the PI substrate without floating over a grooved cavity on a silicon wafer so that the device is more reliable and cheaper. (3) Inert xenon gas was filled into a hemicylindrical chamber instead of the traditional CO2 gas in a rectangular one, so that we could not only increase the device sensitivity but reduce the oxidation effect. (4) A stacked layer of aluminum nitride was inserted under each thermal sensor to increase the device sensitivity. A prototype device was made to prove the performance of the new design.