This paper presents a novel wideband single-pole-single-thru (SPST) switch fabricated by silicon micromachining and operates based on short-circuiting the dominant mode of the rectangular waveguide. The switch has a compact footprint, with a total size of 2×3.5×1.2 mm. The switching mechanism is implemented by a microelectromechanical (MEMS) actuator with an actuation voltage of ~40 V. It has two operating states of propagating and blocking mode. The measured return loss and insertion loss of the switch are 17 dB and 0.7-1.1 dB at 220-290 GHz in the propagating state. The presented switch also has tuning capability to operate with 20 dB return loss at 220-266 GHz. The measured isolation is also 28.5-32.5 dB in the blocking state at the same frequency span.