We study the electrical properties of deep defects in Cu(In,Ga)Se2 (CIGS) by transient photocapacitance (TPC) spectroscopy by varying the Ga concentration in CIGS. Regardless of the Ga concentration, the TPC spectra of CIGS thin-film solar cells at 100 K exhibited a defect level with an optical transition energy of about 0.8 eV. The TPC signals for defect level were quenched by increasing temperature. The activation energy of thermal quenching is estimated to be about 0.3 eV. The variation of the thermal and optical activation energies is caused by the distortions in the local defect configuration.