A magnetic field sensor, comprising: a circular vertical Hall sensing element comprising: a plurality of vertical Hall element contacts arranged over a common implant region in a substrate; and a plurality of vertical Hall elements, each vertical Hall element comprised of a respective group of vertical Hall element contacts selected from among the plurality of vertical Hall element contacts, the magnetic field sensor further comprising; a switching network comprising a plurality of connection nodes, a portion of the plurality of connection nodes coupled to the plurality of Hall element contacts; and a plurality of drive circuits, another portion of the plurality of connection nodes coupled to the plurality of drive circuits, wherein the switching network is operable to couple the plurality of drive circuits to selected vertical Hall element contacts of at least a first one of the plurality of vertical Hall elements, and operable to switch into a normal mode configuration and into a first self-test mode configuration associated with the at least first one of the plurality of vertical Hall elements, wherein, the sensor is configured such that, when in the normal mode configuration, the at least first one of the plurality of vertical Hall elements provides a respective normal mode voltage between vertical Hall element contacts of the at least first one of the plurality of vertical Hall elements, the normal mode voltage responsive to a magnetic field, characterised in that the sensor is configured such that, when in the first self-test mode configuration, the at least first one of the plurality of vertical Hall elements provides a respective first self-test voltage between a respective selected pair of vertical Hall element contacts of the at least first one of the plurality of vertical Hall elements, wherein the first self-test voltage is related to a resistance between vertical Hall element contacts of the at least first one of the plurality of vertical Hall elements, respectively, wherein the first self-test voltage has little or no response to the magnetic field. a circular vertical Hall sensing element comprising: a plurality of vertical Hall element contacts arranged over a common implant region in a substrate; and a plurality of vertical Hall elements, each vertical Hall element comprised of a respective group of vertical Hall element contacts selected from among the plurality of vertical Hall element contacts, the magnetic field sensor further comprising; a plurality of vertical Hall element contacts arranged over a common implant region in a substrate; and a plurality of vertical Hall elements, each vertical Hall element comprised of a respective group of vertical Hall element contacts selected from among the plurality of vertical Hall element contacts, the magnetic field sensor further comprising; a switching network comprising a plurality of connection nodes, a portion of the plurality of connection nodes coupled to the plurality of Hall element contacts; and a plurality of drive circuits, another portion of the plurality of connection nodes coupled to the plurality of drive circuits, wherein the switching network is operable to couple the plurality of drive circuits to selected vertical Hall element contacts of at least a first one of the plurality of vertical Hall elements, and operable to switch into a normal mode configuration and into a first self-test mode configuration associated with the at least first one of the plurality of vertical Hall elements, wherein, the sensor is configured such that, when in the normal mode configuration, the at least first one of the plurality of vertical Hall elements provides a respective normal mode voltage between vertical Hall element contacts of the at least first one of the plurality of vertical Hall elements, the normal mode voltage responsive to a magnetic field, characterised in that the sensor is configured such that, when in the first self-test mode configuration, the at least first one of the plurality of vertical Hall elements provides a respective first self-test voltage between a respective selected pair of vertical Hall element contacts of the at least first one of the plurality of vertical Hall elements, wherein the first self-test voltage is related to a resistance between vertical Hall element contacts of the at least first one of the plurality of vertical Hall elements, respectively, wherein the first self-test voltage has little or no response to the magnetic field.