Abstract: A semiconductor switching device that is suitable for use as a remote isolation device (RID) in telephone networks. The semiconductor switching device is a two-terminal voltage sensitive device that switches from an open-circuit condition to a short-circuit condition at a fixed breakover voltage, appears as an open-circuit below the breakover voltage, and appears as a short-circuit above the breakover voltage. When semiconductor switching devices are installed in a telephone network, they are held in their short-circuit condition by the network voltage supply and do not affect the normal operation of the network but will switch to their open-circuit condition if the network voltage supply is reduced to below the breakover voltage, and therefore, parts of the network may be isolated from each other by reducing the voltage supply. Isolation of the parts of the network from each other facilitates testing for maintenance purposes.