Pentacene-based metal-insulator-semiconductor capacitors with SiO2 and SiO2/Ga2O3 insulators were investigated in the temperature range of 9–300 K. The capacitance-voltage curves of the fabricated capacitors had virtually no hysteresis when using SiO2 as an insulator. The hole concentration values, determined using the Mott–Schottky analysis, were in the range of (1.0–1.3) × 1018 cm–3, depending on the substrate used. It is shown that the hole concentration remains constant over a wide range of frequencies and temperatures. It is shown that the type of the substrate (SiO2 and SiO2/Ga2O3) significantly affects the electrical characteristics of pentacene MIS capacitors. A pentacene film grown on SiO2 substrate was found to have a shallow level with activation energy of about 3 meV. For the case of using SiO2/Ga2O3 substrate, trap levels with activation energies of (5.5–6.0) and (480–570) meV were revealed.