Charges in buried oxide layers formed by wafer bonding were evaluated by capacitance-voltage (C-V) measurements. In this study, silicon-insulator-silicon (SIS) and metal-oxide-silicon (MOS) capacitors were fabricated on bonded wafers. For analyzing C-V curves of SIS structures, C-V simulation programs were developed. From the analysis, the authors concludes that approximately 2×1011/cm2 negative charges were distributed uniformly in the oxide. The effect of the experimental conditions during wafer bonding on generated charges in buried oxides is also discussed