Deep-level transient spectroscopy studies of electronic defect levels in 7-MeV proton-irradiated n-type float-zone Si with a doping of (3-5)x10(12) cm(-3) and oxygen content of similar to10(16)-10(17) cm(-3) have been performed. The thermal stability of the irradiation-induced defects has been investigated for temperatures up to 400 degreesC. It has been found that annealing of the divacancy-related levels, the singly negative, V-2(0/-), and the doubly negative, V-2(-/=), charge states at 220-300 degreesC results in the formation of a new center with singly negative, X(0/-), and doubly negative, X(-/=), charge states. The new center anneals out at 325-350 degreesC during isochronal treatment for 15 min. The capture kinetics studies reveal that the electron capture cross section of X(0/-) is larger than that of V-2(0/-) while the capture cross section of X(-/=) is close to that of V-2(-/=). The transformation of V-2(0/-) and V-2(-/=) into X(0/-) and X(-/=) is very efficient with only a small loss in the peak amplitudes, and the position of the energy levels are close to those of V-2. Hence, it is tempting to suggest that the atomic configuration of the X center is closely related to that of V-2, and a possible identification of X may be the divacancy-oxygen center (V2O).