This paper presents a numerical simulation and experimental results of a one-dimensional thermal inclinometer with sensitivity studies and optimization. The sensor principle consists of one heating resistor placed between two detectors. When the resistor is electrically powered, it creates a symmetrical temperature profile inside a micromachined silicon cavity. By applying a tilt to the sensor, the profile shifts in the same direction of the sensible axis corresponding to the horizontal one-to-one. The temperature profile and the sensitivity according to the CO2 gas pressure have been studied using numerical resolution of fluid dynamics equations with the computational fluid dynamics (CFD) software package Fluent V6.2. The influence of the temperature on the thermo-physical fluid properties has been examined. We have shown that the isothermal temperature profile decreases while the pressure increase. A maximum of the sensitivity at 11 bar for CO2 gas pressure has been obtained taken into consideration of the sensor geometry. Two models have been used to evaluate the thermal boundary layer size function of the evolution of the pressure and theoretically extended to other gases in order to become a parameter field between gas and design. By using micromachined silicon technique, a thermal inclinometer with one pair of detectors placed at 300 μm from the heater has been made. Experimental measurements with CO2 gas corroborate with the numerical simulation and for the optimum pressure, the sensitivity is respectively of 7 °C and 8.1 °C per angle of inclination (°) for an operating power of 75 mW corresponding to a 250 K rise of the heater temperature.