Abstract: An analogue switch formed on a semiconductor substrate has input and output ports, and a first enhancement mode MOS transistor formed in an isolated well in the substrate material and having its gate connected to receive a control signal, and having one end of its conducting channel and its well connected to the input port. A second enhancement mode MOS transistor is formed in an isolated well in the substrate, and has one end of its conducting channel and its well connected to the input port (204), and has its gate connected to the other end of the conducting channel of the first transistor. A third enhancement mode MOS transistor is formed in an isolated well in the substrate, and has its gate connected to receive the complement of the said control signal, and has its conducting channel connected between the output port and the other end of the conducting channel of the second transistor, and has its well connected to one of the supply lines of the switch.