In this study, the effect of quantum dot (QD) sensitization on the luminescent properties of GaAs substrates is investigated by preparing CdSe quantum dots via the chemical deposition method and depositing the quantum dots on the GaAs substrates for sensitization. X-ray diffraction is used to confirm the phase, the QD morphology is characterized via scanning electron microscopy, and the sensitized GaAs substrates are compared with the unsensitized ones through fluorescence spectroscopy. Results show that the prepared CdSe quantum dots are uniform in size (approximately 20 nm) and uniformly adhere to the GaAs substrates. CdSe QD/GaAs forms a type-II band structure. Moreover, quantum dot sensitization increases the carrier concentration on the GaAs substrate surface. The source of each luminescence peak is analyzed via fluorescence spectroscopy. Results illustrate that the band-edge luminescence of the sensitized GaAs substrate is 2.25 times higher than that of the unsensitized GaAs substrate. Furthermore, the defect luminescence of the sensitized GaAs substrate is three times higher than that of the unsensitized GaAs substrate.