We developed a new visual stimulation paradigm for P300-based brain-computer interfaces. The principal idea is to enhance P300 amplitude by modulation of spatial attention to a flickering visual target A small flicker matrix was used for evaluation. Six healthy volunteers participated in experiments, and brain signals were recorded by electroencephalography. We used three basic measures referred to as on-peak, off-peak and peak to compare P300 responses among the participants. We found that compared with existing methods, the proposed stimulation paradigm gave better results in terms of P300 amplitude. The results of this study are expected to contribute to various brain-computer interface applications.