The negative terminal capacitance at high frequencies (usuallyf≫106Hz) in ZnO‐Bi2O3–based varistor systems is attributed to two possible sequential and/or combined sources: (a) piezoelectric grain resonance; and (b) electrode‐lead or contact impedance. These sources are examined using a variation in the geometry of the varistor material and its electrode‐lead configuration. The approximate values of the resonating parameters, designated by an equivalent series lumped inductance‐capacitance‐resistance (Lr‐Cr‐Rr) circuit in parallel with materials’ characteristic capacitanceC0, are extracted employing lumped parameter/complex plane analysis technique for these ac electrical data. At the resonating frequency, the lumped reactance of this series circuit nullifies yielding a resistanceRrreferred to the lumped ZnO grains.