The discharge characteristics of an AC plasma display panel (PDP) with the ridged dielectric structure were investigated. In particular, characteristics such as firing voltage and related wall voltage based on the V-t closed curve measurement were compared in the ridged and conventional dielectric structures. The front plate of the AC PDP with the conventional panel structure is composed of glass, electrodes and dielectric. In the ridged dielectric structure, the middle part of the dielectric layer is eliminated to allow for light to pass through more easily. This structural modification causes the plasma discharge between the two front electrodes to occur at a lower voltage. Meanwhile, as the ridged dielectric structure differs from the conventional dielectric structure, various problems arise if the conventional driving waveform is used. Especially, as the discharge firing voltage characteristics between the scan and sustain electrodes of the ridged dielectric structure is different, it is necessary to modify the reset and address waveforms accordingly. In this study, the V-t closed curves are investigated to compare the discharge firing voltages in the conventional and ridged dielectric structures. Based on the investigation, a modified driving waveform for the ridged dielectric structure was proposed. Using the proposed waveforms, the address discharge time of the ridged dielectric structure was reduced by approximately 200ns.