This paper deals with prebreakdown- and breakdown phenomena in SF6/N-2 gas mixtures, stressed with very fast transient (VFT) voltages. The investigations were performed for positive voltage, frequencies from 3 to 12 MHz, admixtures of N-2 to SF6 from 0 % to 100 % and a pressure range from 0.1 to 0.8 MPa. Gaps with uniform and non-uniform field distribution were investigated.