By including poly-Si/SiO2 and Si/SiO2 interfacial transition (IFT) layers, an excellent agreement in terms of both C-V and J-V characteristics is obtained between the experiment and theory for both polarities of gate voltage (VG) for the first time. The highly precise physical models for gate depletion and gate accumulation bring an oxide thickness extracted from the C-V fitting in a negative VG close to that extracted in a positive VG. It is shown that the physical oxide thickness should be regarded as a distance between the middle points inside the IFT layers in both sides of the gate oxide. In addition, it is found that the tunnel mass is independent of the gate-oxide thickness from 14 to 28 Å. It is also shown that the oxide-thickness dependence of the tunnel mass , - is ascribable to the C-V-J-V fitting only in the case of a negative polarity of VG while neglecting the poly-Si/SiO2 IFT layer.