In this paper, trap levels around the glass transition temperature (Tg) of polymers have been characterized using Thermally Stimulated Current (TSC) technique. Deconvolution on α-peaks of the Tg for PE (-104 °C), plasticized PVC (-35 °C), PMMA (90 °C) and PET (96 °C) were carried out based on the first-order kinetic theory for non-Debye relaxation. Using temperature, T from TSC experimental data, we have successfully separated the α-peaks of the thermoplastic polymers. It is found that the complex curve of α-peaks can composed of four (4) to eight (8) sub peaks. Dominant sub peaks were identified at Tmax = -105 °C, -34 °C, 89 °C and 92 °C for PE, pPVC, PMMA and PET, respectively. These peaks show activation energy, Ea of shallow and deep trap centers ranged from 0.3 eV to 4.6 Ev where they represent the depolarization of localized dipoles and space charges relaxations in the polymers.