High-voltage 4H silicon carbide diodes with breakdown voltages above 3500V were processed and characterized by using different techniques. Measurement results of the electrical properties of p(+)-nu -n and Schottky high-voltage diodes are presented. The achieved Schottky barrier height at room temperature was estimated to be Phi (b) = 1.17 eV from TV measurements. The p(+)-nu -n diodes showed negligible leakage current densities of J(r) less than or equal to 0.5 muA cm(-2) at 1000V reverse bias. We also present a simple model to quantitatively characterize excess currents observed under low forward biases in different diode structures.