A magnetic field sensor formed by a Hall cell having a first, second, third and fourth conduction nodes electrically coupled together by resistive paths. Flowing between the first and second conduction nodes is a control current. In the presence of a magnetic field, a difference of potential due to the Hall effect is generated between the third and fourth conduction nodes. An operational amplifier has an inverting input terminal coupled to the fourth conduction node, a non-inverting input terminal biased at the voltage at the third conduction node, and an output terminal coupled in feedback mode to the inverting input by a feedback resistor. The current generated in feedback through the feedback resistor generates a voltage indicating unbalancing, due to the Hall effect, between the third and fourth conductive nodes, and consequently indicates the intensity of the magnetic field that acts upon the Hall cell.