A high-voltage electronic device comprising high-voltage electrodes, located in a dielectric envelope with an internal surface coated with a material having a conductivity which is greater than the conductivity of the envelope, characterized in that the areas subject to high field strength are coated with composite material, based on a polycrystalline material with a bulk conductivity of particles 10−9 to 10−13 Ohm−1 cm−1, each of which contains a surface nanolayer of bonding inorganic material. The high-voltage electrodes may be placed in a vacuum envelope and fixed on coated insulators. Preferred coating materials include materials from a group of materials comprising; oxides of chromium, boron or zirconium in the form of polycrystalline porous substance with a particle size of 30 nm-30 microns, connected to each other with an inorganic material, for instance silicon oxide (SiO2) with a layer thickness not more than 100 nm.