High voltage 4H-SiC Schottky diodes with single-zone junction termination extension (JTE) have been fabricated and characterised. Commercial 4H-SiC epitaxial wafers with 10, 20 and 45 +m thick n layers (with donor concentrations of 3×1015, 8×1014 and 8×1014 cm-3, respectively) were used. Boron implants annealed under argon flow at 1500°C for 30 minutes, without any additional protection of the SiC surface, were used to form JTE’s. After annealing, the total charge in the JTE was tuned by reactive ion etching. Diodes with molybdenum Schottky contacts exhibited maximum reverse voltages of 1.45, 3.3 and 6.7 kV, representing more than 80% of the ideal avalanche breakdown voltages and corresponding to a maximum parallel-plane electric field of 1.8 MV/cm. Diodes with a contact size of 1×1 mm were formed on 10 +m thick layers (production grade) using the same device processing. Characterisation of the diodes across a quarter of a 2-inch wafer gave an average value of 1.21 eV for barrier heights and 1.18 for ideality factors. The diodes exhibited blocking voltages (defined as the maximum voltage at which reverse current does not exceed 0.1 mA) higher than 1 kV with a yield of 21 %.