Cz-Si doped with boron was implanted at room temperature with 130 keV H2-ions at a high dose of 4×1016 cm−2. The specimens were annealed at a temperature of 450 °C for 10 h in argon ambient. High frequency (1 MHz) C-T and C-V measurements in the temperature range 80–400 K were carried out to study particular features of damage-related centres in the limit of a heavy damage. The presence of damage-related deep-level defects manifest themselves through several unusual features of C-T(V) curves. Sudden jumps of capacitance and hysteresis effects during sweeping temperature/voltage are unusual indeed and have been reported for the first time. Our experiments by filling and emptying deep-level defects with carriers by proper biasing diodes before the temperature/voltage sweep have revealed that the particular features are due to changes in the deep level occupation. The results presented give direct experimental evidence that the damage-induced deep-level defects themselves control the quasi-Fermi level position.