A three-axis magnetic field sensing device, a magnetometer, and methods of fabricating and testing are presented. The magnetometer comprises a plurality of sloped surfaces. A plurality of magnetic sensing units is disposed on the slopes. A magnetic field can be measured by the sensing units. Each of the three orthogonal-axis components of the magnetic field, a Euclidean vector, can then be solved by using a simple algorithm as an expression of the sensing unit measurement values and slope angles. Polarization, testing and characterization of the device could be done by applying a magnetic field along a common axis to all sensing units, along which each sensing unit has sensitivity.