We present the scanning electron-filling modulation reflectance (SEFR) of charged In 0.5Ga 0.5As self-assembled quantum dots. The SEFR is performed by applying a small constant modulation voltage and scanning the dc bias through the quantum dot energy levels. The spectral intensity of the SEFR can be related to the electron density confined in each quantum state, which shows a good agreement with the apparent carrier concentration deduced from the capacitance-voltage measurements. In this study, we find that the transition energy of quantum-dot excited state is about 10 meV smaller than the values obtained from the photoluminescence and electron-filling modulation reflectance. This phenomenon is explained by the Coulomb interactions between the optical excited electron-hole pair and the electrons occupied in the quantum dots.