Novel magnetic field sensors are based on a “cross-shape” ferromagnetic film (FMF) attached to a silicon diaphragm and piezoresistive membrane. The interaction between the magnetic field and the (FMF) generates a deflection of the diaphragm, which changes the piezoresistance and unbalances a Wheatstone bridge. The effect of FMF and silicon diaphragm thickness on the sensor performance is studied by the finite element simulation. The performance of sensor can be improved by optimizing the size of “cross-shape” FMF. These low-cost, low-power sensors are easily integrated with electronic circuits.