A MIS capacitor and a method of making the same. The capacitor includes a semiconductor substrate having a first part having a first conductivity type and contact regions for coupling the first part to an output node. The substrate has dielectric on a surface of the first part and electrodes on the dielectric. The substrate has a second part having a second conductivity type and a third part having the first conductivity type. The third part is coupleable to a supply voltage. The second part is located between the first part and the third part. The first part and the second part form a first p-n junction and the second part and the third part form a second p-n junction. A reference contact is provided for coupling the second part to a reference voltage. A further contact region is provided for coupling the second part to the output node.