Proton-implanted 4H-SiC samples of n-type, have been investigated using Deep Level Transient Spectroscopy (DLTS). Two levels, referred to as S-1 and S-2 have been studied in detail. S-1, and S-2 are located, respectively, at 0.41 eV and 0.71 eV below the conduction band edge. Their extrapolated capture cross-sections are both similar to5x10(-15)cm(2). Furthermore, isochronal annealing performed between 350 and 625K have shown a close one-to-one correlation between the concentration of the two levels. Our results suggest strongly that these levels represent two charge states of the S-center, and the absence of a Pool-Frenkel effect indicates a center of acceptor type.