A Si magnetic field-sensitive split-drain MOSFET has been used to study and analyze the effects of a magnetic field on the charge carrier conduction at liquid-nitrogen temperature. In magnetic field sensors (MFS), a key parameter is the Hall angle, which indicates the current line deviation due to the Lorentz force acting on the charge carriers. If temperature is lowered, the carrier mobility increases, therefore, an increase in carrier deflection is expected. To understand the internal deflection of carriers, and optimize the design of a magnetic field sensor, a semi-analytic model has been developed. Using such a model, a MFS has been fabricated and tested. The first experimental results are presented in this work.