The dependences of sheet resistance (R-s), carrier mobility and sheet carrier concentration on post-implantation annealing temperature and time have been investigated in high-phosphorus (P)-implanted 4H-SiC using Hall effect measurement at room temperature. At an annealing temperature below 1200degreesC, R-s decreases with an increase in annealing time due to the increases in carrier mobility and sheet carrier concentration, but the R-s available for SiC device applications is not obtained using even a long annealing time of 500 min. At an annealing temperature above 1600degreesC, annealing for 30 min causes the R-s to increase due to the decrease in sheet carrier concentration. On the contrary, a R-s of less than 100 Omega/sq. has been achieved at a short annealing time of 30 s because of the extremely high electrical activation of P donors. Based on these results, it is revealed that the decrease in R-s of the P-implanted 4H-SiC is achieved by rapid thermal annealing at high temperature for a short time.