In a system of measuring in which the Hall device is used as input transducer, its stability is essential for transfer constant of system. In this work is analyzed the variation of the charge carriers density on the stability of magnetic sensors realized on the MOS Hall plates. In the same time it is emphasized the way in which the adequate choice of the material properties and geometry of the device allow an increase in its stability. An essential parameter in the setting up of the performance of the measurement systems that use Hall microsensors is the mean square noise equivalent magnetic induction of these devices (NEMI). By using the numerical simulation the values of the NEMI for different structure devices are compared and it is also emphasized the way in which choosing the geometry and the material features allows getting high-performance sensors