In this letter, a highly integrated conjoined device, single shot switch and an exploding foil initiator (S3-EFI) chip, was fabricated with microelectromechanical system scale fabrication methods. Photon Doppler velocimetry was utilized to characterize the behavior of the flyer at firing voltages ranging from 1.00 to 2.40 kV. Electrical characterizations were then performed on the chip to obtain some fundamental parameters, such as current and voltage, and a peak current of 1.73 kA was observed at 1.50 kV. Moreover, ultrafine hexanitrostilbene pellets were detonated over firing voltage range 1.80–1.40 kV. These results demonstrate the feasibility of the chip and pave the way to the non-lead high-voltage discharge circuit. To the best of our knowledge, this is the first time to integrate exploding foil initiator with a high-voltage switch.