An electrically controlled high-speed all-fiber switch is investigated. It is based on a monolithic Mach-Zehnder interferometer using a Gemini fiber. The fiber is provided with internal electrodes for active control of the phase using high-voltage electrical pulses. The demonstrated switching speed is 20 ns. The monolithic design guarantees that the off- and on-states are attained simultaneously for a broad range of wavelengths (50 nm). The interferometer can be switched-off using a second electrode, providing a 15 ns long optical pulse.