In this paper, the design and development of an electrostatically actuated micro-electromechanical systems (MEMS) device for the tensile test of Si nanowires (NWs) are described. The device is composed of a comb-drive electrostatic actuator for generating uniaxial tensile force, capacitive sensors for measuring tensile force and displacement, an electrothermal actuator with a ratchet for clamping and releasing a sample stage, and a force calibration mechanism. The resolution of the tensile elongation measurement is 1 nm, determined by a resolution of 0.1 fF on an LCR meter. The tensile force is derived from the displacement and the spring constant of the support beams of the driven sensor. The theoretical resolution of tensile force measurements ranges from 10 to 263 nN, depending on the stiffness of the specimen. Electrical insulating structures for minimizing electrical signal noise are designed to accurately measure the capacitance change of the two capacitive sensors. To demonstrate these possibilities, Si NWs fabricated using a focused ion beam (FIB) were characterized using a scanning electron microscope (SEM). The Young's modulus and fracture strength were 127.7 and 5.4 GPa, respectively, indicating that FIB damage affects these mechanical characteristics.