A solid-state image sensor comprises an n-type silicon substrate (11), a p-type silicon layer (12) formed on the substrate (11), a plurality of nMOS transistors (1), a field insulating film (13) for separating the nMOS transistors (1) and a buried insulating film (20) provided between the substrate (11) and the field insulating film (13). The buried insulating film (20) serve to prevent electrons from flowing between the adjacent nMOS transistors (1). Accordingly, occurrence of a color mixture phenomenon, a blooming phenomenon or a smear phenomenon can be suppressed. In addition, when a p-type junction layer (21) is provided on the substrate (11) and a bias power supply (19) is connected between them, and when the voltage is adjusted, the red color sensitivity of a photodiode consisting of an n-type source region (16) in each nMOS transistor (1) can be uniformly and easily adjusted.