The paper reports on the influence of processing on microstructure and electrical properties of multilayer varistors based on zinc oxide doped with Bi₂O₃, Sb₂O₃, Co₂O₃, MnO, Cr₂O₃, B₂O₃, and SiO₂. 0.5-1 wt% of AlF₃-CaB₄O₇ was used as a new effective sintering aid. The behavior of green laminates during heating was characterized using differential thermal analysis and a heating microscope. As revealed by XRD, SEM, and EDS methods, the varistor layers are composed of ZnO grains of 1-5 μm size, submicrometer spinel and pyrochlore grains situated at the ZnO grain boundaries, and nanometric Bi₂O₃-rich films surrounding ZnO grains. Complex impedance studies carried out in the frequency range of 0.01 Hz-2 MHz at temperatures changing from -30 to 150 ℃ imply the formation of semiconducting grains and insulating grain boundaries. Frequency dependence of dielectric permittivity shows a high plateau at lower frequencies, typical for barrier layer capacitance effect. The fabricated multilayer varistors show nonlinear current-voltage characteristics with a high nonlinear coefficient of 26-38. The breakdown voltage was found to decrease within the range of 66-130 V with sintering temperature increasing from 1000 to 1100 ℃. Good surge current capability of the varistors was confirmed by the tests using 8/20 μs pulses.