The broad applications of ultrawide-band signals and terahertz waves in quantum measurements, imaging and sensing techniques, advanced biological treatments, and very-high-data-rate communications have drawn extensive attention to ultrafast electronics. In such applications, high-speed operation of electronic switches is challenging, especially when high-amplitude output signals are required. For instance, although field-effect and bipolar junction devices have good controllability and robust performance, their relatively large output capacitance with respect to their ON-state current substantially limits their switching speed. Here we demonstrate a novel on-chip, all-electronic device based on a nanoscale plasma (nanoplasma) that enables picosecond switching of electric signals with a wide range of power levels. The very high electric field in the small volume of the nanoplasma leads to ultrafast electron transfer, resulting in extremely short time responses. We achieved an ultrafast switching speed, higher than 10 volts per picosecond, which is about two orders of magnitude larger than that of field-effect transistors and more than ten times faster than that of conventional electronic switches. We measured extremely short rise times down to five picoseconds, which were limited by the employed measurement set-up. By integrating these devices with dipole antennas, high-power terahertz signals with a power–frequency trade-off of 600 milliwatts terahertz squared were emitted, much greater than that achieved by the state of the art in compact solid-state electronics. The ease of integration and the compactness of the nanoplasma switches could enable their implementation in several fields, such as imaging, sensing, communications and biomedical applications.