A new driving waveform was proposed in order to stabilize the driving characteristics of a high-efficacy ac plasma-display panel (PDP) with a coplanar gap of 200 μm and an auxiliary electrode. To stabilize the reset and address discharge, an erase pulse was applied to the auxiliary electrode instead of the sustain electrode after the sustain period. The write pulse was applied to the scan electrode, and a reset discharge was induced between the scan and auxiliary electrodes. As a result, the minimum address voltage could be reduced to a level similar to that achieved with a conventional ac PDP with a coplanar gap of 80 μm. Furthermore, the address-discharge time lag of the ac PDP with a coplanar gap of 200 μm was improved to a level that is comparable with that of the ac PDP with a coplanar gap of 80 μm