Al-implanted p-type 4H-SiC layers with different conditions of implantation and annealing temperatures are formed, and the temperature dependence of the hole concentration p(T) in the p layer is obtained from Hall-effect measurements. In order to determine the reliable acceptor density (N-A) from p(T), it is found that the Fermi-Dirac distribution function is not appropriate and that a distribution function including the influence of the excited states of Al acceptors is required. This is because the Al acceptor level in SiC is deep (similar to 180 meV) and because its first excited state level, which is calculated by the hydrogenic model, is still deep (similar to35 meV), which is close to the acceptor level of B in Si. It is demonstrated that the proposed distribution function is suitable for obtaining the actual relationship between N-A and p(T).