The rapid progress in high capacity communication systems is reaching extremely high data rates of 100 Gb s−1, which demands electronic switches with cut-off frequencies well above 1 THz. The excellent electron transport properties of III-V heterojunctions could potentially enable terahertz devices, however, the high parasitic capacitances and contact resistances in traditional ultra-scaled electronic devices, such as transistors and diodes, hinder their potential. Here we demonstrate that the fast switching of displacement fields strongly confined in a few-nanometers-thin crystal between a textured metal and an electron sheet, so called displacement-field nano-switch, can provide cut-off frequencies above 8 THz, enabling an efficient switching of terahertz signals. The device offers extremely low ON state resistances approaching 100 Ω μm, low parasitic capacitances in range of 100 aF μm−1, excellent impedance matching capability, and fast switching times down to 10 ps. We demonstrate the application of these devices for high data rate modulation and mixing. The outstanding performance and integration capability of displacement-field nano-switches pave the way towards mm-wave and terahertz integrated circuits with applications in 5G and 6G communications, among others.