For many applications in micro-electromechanical systems (MEMS), having high aspect ratio sensors or actuators can improve performance, increase sensitivity, and lower power consumption. Micro- and nano-fabrication technology can be used to generate these high aspect ratio MEMS. Etch rate, profile, selectivity, and uniformity could vary as aspect ratio becomes higher since plasma etching characteristics depend on aspect ratio of microstructures. These variations could affect MEMS performance. In this talk, key issues to provide precise control in MEMS fabrication by plasma processing will be discussed. High aspect ratio MEMS including micromirrors for optical switching arrays, submicrometer resonators for accelerometers, sharp tips for emitters or scanning probes, and microheaters for micro-gas chromatography systems will be reviewed.