The mechanism of the reduction in the electron concentration in lightly N-doped n-type 4H-SiC epilayers by 200 keV electron irradiation is investigated. From the temperature dependence of the electron concentration, n(T) , in the epilayer before and after irradiation with fluences ( Φ ) of 1 x 1016 and 2 x 1016 cm-2, the densities and energy levels of donors and the compensating density are determined by a graphical peak analysis method. In the non-irradiated case, the density of N donors located at hexagonal C-sublattice sites ( NHN ) is 5.1 x 1014 cm-3, and the density of N donors located at cubic C-sublattice sites ( NKN ) is 4.7 x 1014 cm-3. NHN decreases with increasing Φ , and it becomes less than 1014 cm-3 at Φ = 2 x 1016 cm-2, whereas NKN decreases slightly to 4.1 x 10 cm-3 at Φ = 2 x 1016 cm-2. This suggests that N donors at hexagonal C-sublattice sites are less radiation-resistant than N donors at cubic C-sublattice sites.