Micromachined sensors, also called electromechanical systems (MEMS), are delivered in several billions of devices per year at sub-1 Euro cost for several applications, including mobile phones, toys, cars. Such a large-scale utilization has been enabled by the key advantages of micromachining as a manufacturing technology, which are: large-scale parallel processing, very high level of miniaturization and integration, excellent product uniformity and very high volume manufacturing capability. In contrast to that, current THz technology is still primarily utilizing CNC-milling, which is a sequential and not scalable fabrication technology. This paper summarizes the state of the art in silicon micromachining, discusses advantages and disadvantages and describes several millimeter-wave and submillimeter-wave devices and systems implemented in micromachined-waveguide technology, including very-low loss filters, OMTs, couplers, integrated absorbers/attenuators, switches