A solid-state image sensor includes a pixel area and a peripheral circuit area. The pixel area includes a first MOS, and the peripheral circuit area includes a second MOS. A method includes forming a gate of the first MOS and a gate of the second MOS, forming a first insulating film to cover the gates of the first and second MOSs, etching the first insulating film in the peripheral circuit area in a state that the pixel area is masked to form a side spacer on a side face of the gate of the second MOS, etching the first insulating film in the pixel area in a state that the peripheral circuit area is masked, and forming the second insulating film to cover the gates of the first and second MOSs and the side spacers.