The negative differential capacitance (NDC) of Schottky diodes with layers of InAs quantum dots (QDs) has been clearly observed at room temperature. The frequency dependence of the NDC is investigated. The measured peak capacitances of NDC decay rapidly at the testing frequencies higher than a few kilohertz. A kinetic model considering the testing signal is proposed and the capture rates of QDs are extracted. The simulation result is quantitatively consistent with the experimental data when the charging effect in QDs is included.