In this study, we focus on the difference behavior of the gate-channel capacitance (Cgc) characteristics in the inversion-mode (IM) and the accumulation-mode (AM) SOI MOSFETs. We experimentally demonstrate that the gate-channel capacitance in the AM MOS device is obviously larger than that in IM MOS device using the same gate insulator on the same wafer. The increase of the Cgc in AM MOSFETs is much more remarkable as downscaling the gate insulator due to the different inversion and accumulation layer quantization effect and poly-Si gate depletion effect. As the result, the current drivability has been obviously improved in the AM MOSFETs resulted from its vastly increased gate-channel capacitance, especially in the MOSFETs with the ultrathin gate insulator.