A post implantation microwave annealing technique has been applied for the electrical activation of Al+ implanted ions in semi-insulating 4H-SiC. The annealing temperatures have been 2000-2100 C. The implanted Al concentration has varied from 5 x 10 19 to 8 x 10 20 cm-3. A minimum resistivity of 2 x 10-2 Ω∙ cm and about 70% electrical activation of the implanted Al has been measured at room temperature for an implanted Al concentration of 8 x 10 20 cm-3 and a microwave annealing at 2100 C for 30 s.