The microplasma modes generated in a plasma display with a coplanar gap and an auxiliary electrode were investigated using the discharge current peak time (discharge delay) and discharge current. Three types of modes were classified as follows: Mode 1) showed a decrease in both the discharge current and the discharge delay, Mode 2) showed a decrease in the discharge current and an increase in the discharge delay, and Mode 3) showed an increase in the discharge current and a decrease in the discharge delay. The infrared efficiency increased in Modes 1) and 2) with an increase in the auxiliary pulse voltage. However, in Mode 3), the IR efficiency started to decrease. According to the measurement results, Modes 1) and 2) are suitable for microplasma generated in a coplanar gap with an auxiliary electrode to obtain high efficacy.