The peculiar variation of breakdown voltage vb with pressure p in compressed SF6 due to coronastabilization of the applied field is well pronounced in rod to plane gaps, Fig. (1). In this paper, the spacecharge mo&ed field has been calculated and a simple criterion based on the gapminimumfieldis proposed for breakdown in the rising straight part of the vb-p characteristic . This calls at first for assessment of the corona onset voltage. For pressures greater than the critical pressure breakdown occurs without any preceding corona discharges and the breakdown voltage is theoretically predicted. The calculated corona-onset V, and breakdown voltages agreed with those measured experimentally within f 10 Yo.