The electrical conductivity, thermally stimulated depolarization current as well as the current-voltage characteristics were measured from 77 K to 350 K. The obtained results are correlated with the Raman scattering spectroscopy and ESR spectra. In Al-Si-diamond layer-Al structures three (for B-doped diamond layers) or two (for no B-doped diamond layers) TSC peaks in the temperature range between 100 and 300 K are observed. They correspond to trap levels with a thermal activation energy of 0.03-0.06 eV, 0.13-0.18 eV and 0.6-0.65 eV.