Integrated circuit devices include operational circuits that are configured to operate from power supply voltages and from high voltages that are generated in the integrated circuit device from the power supply voltages. A circuit for measuring the high voltages is also provided in the integrated circuit. The circuit includes a common high voltage measurement pad and high voltage switch units connected to the common high voltage measurement pad. A respective high voltage switch unit is configured to transmit a corresponding one of the high voltages to the common high voltage measurement pad in response to a corresponding enable signal. The operational circuits may be non-volatile memory cells, such as flash memory cells. Related methods of measuring high voltages in an integrated circuit device are also described.