High-voltage (900 V) 4H-SiC Schottky-barrier diodes (SBD) terminated with guard pnjunction were fabricated and investigated. The guard pn-junction was formed by room temperature boron implantation followed by high temperature annealing. Owing to the transient enhanced boron diffusion during anneal, the depth of guard pn-junction is about 1.7 μm, that is approximately 1 μm deeper than the expected average range of 11B ions in 4H-SiC. The maximum reverse voltage of 4H-SiC SBD produced has been found to be limited by the avalanche breakdown in cylindrical portion of planar pn-junction. The value of the breakdown voltage of 910 V is close to theoretical one calculated for the dopant density = 2.5×1015 cm-3, n-base thickness d = 12.5 μm and junction curvature rj = 1.7 μm. Dynamic (pulse) reverse current-voltage characteristics were measured in the breakdown regime. It was found that dynamic breakdown voltage increases with shortening the pulse duration. Due to homogeneous avalanche breakdown at the edge of the quard pn-junction and high differential resistance in the breakdown regime, the diodes under test are able to withstand, with no degradation, pulse reverse voltage at least 1600 V.