The carbon vacancy (V C) is a minority carrier lifetime controlling defect in 4H-SiC and it is formed during high temperature treatment. In this study, we have performed heat treatment on two sets of n-type 4H-SiC epitaxial samples. The first set was isothermally treated at 1850 C to follow the evolution of V C as a function of time. The V C concentration is not affected by changing the duration. Samples of the other set were treated at 1950 C for 10 min, but with different cooling rates and a reduction of the V C concentration was indeed demonstrated by lowering the cooling rate. The V C concentration in the slow-cooled sample is about 2 times less than in the fast-cooled one, reflecting a competition between equilibrium conditions and the cooling rate.