Due to cubic boron nitride (cBN) extraordinary properties like a high Debye temperature, wide band gap (6.4 eV), elasticity modulus, high thermo-conductivity and mechanical strength, thermal and irradiative resistance the material has been considered as the prospective one for solid state electronics. CBN semiconductor properties investigations were started many years ago, but systematic dates about them have been absent. Electro-conductivity, thermo-stimulated conductivity, current-voltage characteristics and electro-conductivity dependences on temperatures for polycrystalline cBN. are investigated in present work. Undoped polycrystals were synthesized from pyrolytic boron nitride under high pressure/high temperature conditions. CBN n-type was realized by sulfur and aluminium doping. The curves of electroconductivity - temperature dependences have typical activation character at low temperatures. However the electro-conductivity drastically increases (of 2-4 orders in magnitude) for all doped and weakly doped samples at temperature about 670K. The current-voltage characteristics in logarithmic scales investigated at room and low (up to 570K) temperatures consist from some linear plots. An electrical instability appears as current multiplication of 2-4 orders at temperatures beyond 670K. Such a "switch on" of low resistance cBN state preferably appears in sulfur doped polycrystalline samples. The thermo-stimulated electro-conductivity investigations of cBN undoped samples allow to establish three local levels in energy region from 1.0 to 2.2 eV.