The invention relates to a magnetic field sensor comprising a substrate having a first side (S1). The substrate comprises at the first side (S1) a silicon comprising semiconductor layer (P-SUB) which comprises a buried N-well (DNW). A bipolar transistor having an emitter region (PE+, NE+), a base region (PB+, NB+), and a first collector region (CLR1) and a second collector region, is provided in the silicon comprising semiconductor layer (P-SUB). The emitter region (PE+, NE+) is located at the first side (S1) above the buried N-well (DNW). According to the invention the bipolar transistor is arranged such that, in operation, a part of an emitter current (IEM) that traverses the base region (PB+, NB+) is distributed over the first and second collector regions (CLR1, CLR2) obtaining a first and a second collector current (ICL1, ICL2), wherein a difference between the first and second collector currents (ICL1, ICL2) is determined by a magnetic field component (B x, B z ) perpendicular to a current plane. A bipolar magneto-transistor structure is obtained which is compatible with triple-well technology and that is sensitive to magnetic fields in a direction perpendicular to the current plane. The magnetic field sensor is compatible with triple-well technology and has a high linearity and a high sensitivity. The invention further relates to an integrated circuit comprising such magnetic field sensor (Snsr) and a card provided with such integrated circuit.