In Algeria, the residential sector registries a high rate of energy consumption which requires an important action for rationalizing this charge and integrating renewable energies. Particularly, the geothermal energy with its less intermittence presents an attractive candidate to reinforce energy-saving and building thermal comfort. In this paper, geothermal energy is used to create a favorable environment for creating a better life inside a semi-buried building during the very hot period in the desert climate of southern Algeria. The cooled room is buried in rocky soil until 3 m depth, and only 0.5 m of the room high is above the ground level. The upper parts of southern and northern room walls are provided by small windows for aeration and lighting purposes. Inside room the air flow is modeled by Navier-Stocks and energy equations. The computational domain is taken as 3D design, and the prediction of temperature is calculated by ANSYS-Fluent code. For the base case, at 2 m height, the indoor temperature fluctuates between 30 and 33°C which is in good concordance with experimental data. For reducing the indoor temperature, some simple design modifications are introduced and a small ventilation system is installed. The new results show that the indoor temperature does not exceed 25 °C at the height of 2 m, therefore the temperature for height between 2 and 3 m it fluctuates between 25 and 26 °C. This indoor thermal behavior ensures acceptable cooling with negligible electricity consumption.