EPR measurements at 37 GHz and 77K have been made on undoped High Purity Semi-Insulating 4H-SiC in the dark and after illumination. Two intrinsic defects with donor-like behavior have been detected by EPR. Temperature dependent Hall effect measurements confirm that the conduction is n-type in these samples. It is suggested that that the deep donor-like defects with S =1/2 are the V-Si(3-) and probably V-C(1-) defects and that they might be responsible for the compensation of shallow nitrogen and boron in SI- 4H SiC.