In this paper we investigate the thermo mechanical behavior of a silicon piezoresistive pressure sensor. The totally built-in thin silicon membrane sensor response computation under constant and uniform pressure assuming small deflections have been determined using Finite Element Analysis (FEA) made in COMSOL. The model solved by COMSOL environment takes into account the entire sensor and thermal effects caused by the manufacturing process of the device. This allows a better understanding and monitoring the thermal drifts that can affect the sensor. COMSOL is easy to implement, ensures a good result in matters of affinity and it allows us to be closer to the real structure of the sensor with extreme flexibility. A temperature study of sensor was performed and the results allow us to predict the sensor behavior against temperature and to minimize this effect by optimizing the doping concentration. Finite Element Analysis (FEA) provides a reliable tool to carry out the required parametric studies in order to optimize the sensor performance.