A glow-to-arc transition of rarefied plasma that controls the ultimate performance of a vacuum interrupter depends on the state of remaining plasma in the contact gap after current zero. In this study, the electron temperature and the ion density of residual plasma of a magnetically stabilized high-current vacuum arc were measured by the electrostatic (Langumuir) probe method. As a result of measurements, electron temperature was of the order of 3eV with a uniform space distribution and was independent of the arc current. The space distribution of the ion density was diffusion-controlled mode, contrary to the confined mode in the steady state condition. The ion density was independent of peak arc current and increased linearly with current zero gradients. The density of the copper ions decayed with a time constant of about 2 µs.