Aluminum ion (Al+) and boron ion (B+) implantation into 4H-SiC and the characteristics of implanted pn junctions have been investigated. Three groups of diodes with planar structures were fabricated by employing Al+ and B+ implantation. A SiC pn diode fabricated by shallow Al+ and deep B+ implantations has exhibited a high breakdown voltage of 2900 V with a low on-resistance of 8.0 mOmegacm(2) at room temperature. The diodes fabricated in this study showed a positive temperature coefficient of breakdown voltage.