An apparatus including an electrostatic discharge protection device comprising: a semiconductor device having collector , base and emitter regions arranged at an upper surface of a semiconductor substrate to form a horizontal transistor, wherein the collector region is doped with a first impurity of a first conductivity type, the base region is doped with a second impurity of a second conductivity type opposite the first type and the emitter region is doped with an impurity of the first conductivity type, wherein the emitter region is located within the base region , and a fourth region of semiconductor is provided beneath the base region and separated from the base region by an intervening region, and the fourth region and the intervening region are doped with an impurity of the second type with the fourth region being more heavily doped than the intervening region, and wherein the collector region is horizontally separated from the base region only by a separation region, the separation region being a portion of said intervening region, the base region being more heavily doped than the separation region, and wherein the electrostatic discharge protection device is adapted such that: the separation region provides a separation between the collector and base regions to define a trigger voltage to cause the electrostatic discharge protection device to become conducting; and a spatial parameter of the base region controls a holding voltage of the electrostatic discharge protection device, where the spatial parameter is one of a width of the base region, an area of the base region or a volume of the base region . a semiconductor device having collector , base and emitter regions arranged at an upper surface of a semiconductor substrate to form a horizontal transistor, wherein the collector region is doped with a first impurity of a first conductivity type, the base region is doped with a second impurity of a second conductivity type opposite the first type and the emitter region is doped with an impurity of the first conductivity type, wherein the emitter region is located within the base region , and a fourth region of semiconductor is provided beneath the base region and separated from the base region by an intervening region, and the fourth region and the intervening region are doped with an impurity of the second type with the fourth region being more heavily doped than the intervening region, and wherein the collector region is horizontally separated from the base region only by a separation region, the separation region being a portion of said intervening region, the base region being more heavily doped than the separation region, and wherein the electrostatic discharge protection device is adapted such that: the separation region provides a separation between the collector and base regions to define a trigger voltage to cause the electrostatic discharge protection device to become conducting; and a spatial parameter of the base region controls a holding voltage of the electrostatic discharge protection device, where the spatial parameter is one of a width of the base region, an area of the base region or a volume of the base region . the separation region provides a separation between the collector and base regions to define a trigger voltage to cause the electrostatic discharge protection device to become conducting; and a spatial parameter of the base region controls a holding voltage of the electrostatic discharge protection device, where the spatial parameter is one of a width of the base region, an area of the base region or a volume of the base region . <EOS>