a magnetic field sensor apparatus for determining two or three components of a magnetic field includes at least one wheatstone bridge with two half - bridges , wherein each half - bridge includes at least two bridge resistors , and at least one of the two bridge resistors is a magnetic - field - sensitive resistor with respect to a magnetic field component in an x / y magnetic field sensor plane . arranged symmetrically between the two magnetic - field - sensitive bridge resistors is a ferromagnetic flux concentration element which generates magnetic field components which are anti - symmetric with respect to a z magnetic field component oriented perpendicular to the x / y magnetic field sensor plane and are in the x / y magnetic field sensor plane . a coordinate aspect proposes a method for determining a two - dimensional or three - dimensional orientation of an external magnetic field by such a magnetic field sensor apparatus .