Transitions between the streamer and spark modes affect the stability of gas–liquid discharges, limiting their practical applications, while the nature of such transitions is poorly understood. Here we clarify the often neglected effect of a dielectric on the gas–liquid discharge stability, using direct and indirect grounding configurations. Discharge modes and plasma characteristics in these two configurations are investigated. The discharge appears in a transient spark mode in the direct grounding while in a streamer mode in the indirect case. It is shown that the dielectric significantly improves the discharge stability. The gas temperature and electron density in the transient spark are 380 K and 1017/cm3 with a 30 kV pulse voltage, respectively, which are higher than those in the streamer mode.