Offset is observed in the charge–voltage (Q–V) or internal charge–phosphor field (Q–Fp) characteristics of certain alternating-current thin-film electroluminescent (ACTFEL) devices. This offset arises from a displacement along the voltage axis of a transient curve measured across a sense capacitor in the electrical characterization setup. A procedure for adjusting this offset is proposed that allows ACTFEL devices manifesting offset to be meaningfully analyzed. Two possible sources of offset are deduced from simulation and are associated with an asymmetry in the interface state energy depths at the two phosphor–insulator interfaces or with an asymmetry in the location of space charge generation in the phosphor.