A semiconductor device having a solid-state image sensor which can prevent inter-pixel crosstalk more reliably. The device includes: a semiconductor substrate having a main surface; a first conductivity type impurity layer located over the main surface of the substrate; a photoelectric transducer including a first conductivity type impurity region and a second conductivity type impurity region which are joined to each other over the first conductivity type impurity layer; and transistors which configure a unit pixel including the photoelectric transducer and are electrically coupled to the photoelectric transducer. At least part of the area around the photoelectric transducer in a plan view contains an air gap and also has an isolation insulating layer for electrically insulating the photoelectric transducer and a photoelectric transducer adjacent to it from each other. The isolation insulating layer abuts on the top surface of the first conductivity type impurity layer.