The dominant carbon‐related radiation damage center in silicon was studied in detail by deep level transient spectroscopy. Samples with different carbon and oxygen content were implanted with gradually increasing proton fluence. Two energetically closely spaced levels were revealed and tentative identities were assigned. One atET+EV=0.344 eV (&sgr;p=1.1×10−16cm2) is assigned as the C+Oicomplex, and that atET+EV=0.370 eV (&sgr;p=8×10−18cm2) is assigned as the Cs‐Sii‐Cscomplex. It was shown that the concentration of these defects is correlated to the total concentration of carbon in the crystal.