Summary form only given. The improvement of the optical quality of semiconductor quantum dots (QDs) grown by Stranski-Krastanow mode is able to realize the QD based optical devices. Owing to the optimization of the growth condition, the performance of QD lasers is improved and becomes to exceed that of quanturn-well lasers. The homogeneous line-width affects the performance of the QD laser such as modulation characteristics and also contains the information on carrier-phonon interaction, carrier-carrier interaction and so on. In the operation of QD laser at room temperature, many carriers injected in and around the QD and the carrier-carrier interaction would lead to the substantial broadening of the linewidth. Employing a high sensitive near-field scanning optical microscope, we performed the single-QD PL spectroscopy at room temperature and discussed the carrier-carrier interaction through the excitation power dependent spectral shift and broadening.