241 6009 53235 Frequency-dependent capacitance-voltage (C-V) and impedance-spectroscopy characteristics of nanoplate capacitive field-effect electrolyte-insulator-silicon-on-insulator (EISOI) structures with various thicknesses (30, 60 and 350 nm) of the top p-Si layer are investigated for the first time. The frequencydependent C-V curves of EISOI structures show an unusual behaviour, which significantly differs from that of conventional EIS structures. Due to the large series resistance of the nanoplate top Si, the C-V curves of the EISOI structures show stronger frequency dependence in the accumulation region. In addition, C-V curves show typical low-frequency behaviour even at higher frequencies (up to 8 kHz). An equivalent circuit of an EISOI structure is discussed taking into account the series resistance of the nanoplate top Si.