240 GHz electron paramagnetic resonance (EPR) measurements of as-grown nominally semi-insulating 4H SiC detected two well-separated centers ID1 and ID2. The EPR parameters of ID1 and ID2 coincide with that of EI5 and EI6 centers previously detected in 2-MeV electron-irradiated p-type 4H SiC:Al by 95 GHz EPR (Son et al.). The defects in irradiated material were assigned to a positively charged carbon vacancy (EI5) and silicon antisite (EI6), respectively. Increased separation between the two centers at 240 GHz and the absence of additional radiation-induced spectral lines in the as-grown, unirradiated SiC facilitated analysis of the defect structure. Our data support that the ID1 center is a carbon vacancy-related defect, but is not consistent with the assignment of the ID2 center to a silicon antisite. The ID2 spectrum is best fit as another carbon vacancy-related defect. Illumination with light below 1400 nm quenched both ID1 and ID2 simultaneously, suggesting that the defect energy levels are nearly the same. © 2003 The American Physical Society.