We investigated the influences of the AC response with interface/bulk-oxide traps near the conduction band (CB) and a low effective density of states (DOS) on the accumulation capacitance C-acc of an n-type InGaAs metal-oxide-semiconductor (MOS) capacitor. We found that the capacitance associated with the interface traps inside the CB significantly increases C-acc compared to the C-acc value constrained by a low DOS. These results indicate that accurate characterization inside the CB and considering the capacitance due to the interface traps inside the CB in the MOS capacitance-voltage curves are indispensable for accurate characterization of InGaAs MOS interface properties. (C) 2016 The Japan Society of Applied Physics