To form deep (greater than or equal to2 mum) p-well regions for several-kV SiC power devices, MeV ion implantation of Al and B into 4H-SiC has been systematically investigated. The 3 mum-deep box profiles were formed through MeV Al+- and B+-implantation, and the electrical activation was investigated. The activation ratio of Al was larger than that of B, and each activation ratio was improved with C+ co-implantaion. Pn junction diodes were fabricated by MeV Al+- and B+-implantations. The B+-implanted diodes showed better reverse characteristics than the Al+-implanted diodes.