AbstractThis paper describes emission characteristics of MOS (metal–oxide–semiconductor) electron tunneling cathodes and Si field emitters, and shows that their characteristics reflect the energy band structures of the semiconductor and the electron transport in an incorporated semiconductor device. In addition, it proposes hybrid electronics combining solid‐state device and vacuum device technologies, and shows that this approach provides highly efficient high‐frequency devices with coverage from the microwave to the optical wave regions. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(5): 1–9, 2001