A probe based on the measurement of the electrical impedance has been developed to determine the phase hold‐ups in gas‐solid‐liquid stirred tank reactors. The idea was to take advantage of the complex nature of electrical impedance to derive two independent data (conductance and capacitance) from one measurement. Particular attention has been paid to the calibration of the probe and two semi‐empirical equations have been given to relate measurement to hold‐ups. Subsequently, experiments were performed on three‐phase and two‐phase (gas‐liquid and solid‐liquid) systems and the results have been critically analysed.