A voltage reference comprising: a circuit on a single die configured to generate a substantially constant reference voltage (103; 603), the circuit including an arrangement of a first and a second group of individual transistors (Q1, Q2) configured such that: the first group of individual transistors collectively function as a first composite transistor in the circuit with a first emitter area equal to the combined areas of the emitters of the first group of individual transistors; and the second group of individual transistors collectively function as a second composite transistor in the circuit with a second emitter area that is equal to the combined areas of the emitters of the second group of individual transistors and that is greater than the first emitter area, wherein: the circuit is configured such that the stability of the constant reference voltage (103; 603) is dependent upon the stability of the ratio between the first emitter area and the second emitter area; the first group of individual transistors is not at the center of an arrangement of the second group of individual transistors; and the constant reference voltage (103; 603) varies due to thermal hysteresis by less than 200 parts per million over a 40 degree centigrade temperature range. a circuit on a single die configured to generate a substantially constant reference voltage (103; 603), the circuit including an arrangement of a first and a second group of individual transistors (Q1, Q2) configured such that: the first group of individual transistors collectively function as a first composite transistor in the circuit with a first emitter area equal to the combined areas of the emitters of the first group of individual transistors; and the second group of individual transistors collectively function as a second composite transistor in the circuit with a second emitter area that is equal to the combined areas of the emitters of the second group of individual transistors and that is greater than the first emitter area, the first group of individual transistors collectively function as a first composite transistor in the circuit with a first emitter area equal to the combined areas of the emitters of the first group of individual transistors; and the second group of individual transistors collectively function as a second composite transistor in the circuit with a second emitter area that is equal to the combined areas of the emitters of the second group of individual transistors and that is greater than the first emitter area, wherein: the circuit is configured such that the stability of the constant reference voltage (103; 603) is dependent upon the stability of the ratio between the first emitter area and the second emitter area; the first group of individual transistors is not at the center of an arrangement of the second group of individual transistors; and the constant reference voltage (103; 603) varies due to thermal hysteresis by less than 200 parts per million over a 40 degree centigrade temperature range. the circuit is configured such that the stability of the constant reference voltage (103; 603) is dependent upon the stability of the ratio between the first emitter area and the second emitter area; the first group of individual transistors is not at the center of an arrangement of the second group of individual transistors; and the constant reference voltage (103; 603) varies due to thermal hysteresis by less than 200 parts per million over a 40 degree centigrade temperature range.