A semiconductor device comprising: a first semiconductor section including a first wiring layer at one side thereof, the first semiconductor section further including a photodiode ; a second semiconductor section including a second wiring layer at one side thereof, the first and second semiconductor sections being secured together; a third semiconductor section including a third wiring layer at one side thereof, the second and the third semiconductor sections being secured together such the first semiconductor section, second semiconductor section, and the third semiconductor section are stacked together in a manner such that the first wiring layer faces the second semiconductor section and the third wiring layer faces the second semiconductor section; a first conductive material electrically connecting the first wiring layer and the second wiring layer, and a second conductive material electrically connecting the second wiring layer and the third wiring layer such that the electrically connected wiring layers are in electrical communication; a pad electrode configured to be used as one end of a wire related to input and output of a signal with an external device, wherein the pad electrode is disposed such that light from one or more transistors residing in the second semiconductor section is blocked; the pad electrode is electrically connected to the first conductive material and to the second conductive material ; and either: the second wiring layer faces the third wiring layer and the pad electrode is formed in the first wiring layer of the first semiconductor section, or the second wiring layer faces the first wiring layer and the pad electrode is formed in the second wiring layer of the second semiconductor section. a first semiconductor section including a first wiring layer at one side thereof, the first semiconductor section further including a photodiode ; a second semiconductor section including a second wiring layer at one side thereof, the first and second semiconductor sections being secured together; a third semiconductor section including a third wiring layer at one side thereof, the second and the third semiconductor sections being secured together such the first semiconductor section, second semiconductor section, and the third semiconductor section are stacked together in a manner such that the first wiring layer faces the second semiconductor section and the third wiring layer faces the second semiconductor section; a first conductive material electrically connecting the first wiring layer and the second wiring layer, and a second conductive material electrically connecting the second wiring layer and the third wiring layer such that the electrically connected wiring layers are in electrical communication; a pad electrode configured to be used as one end of a wire related to input and output of a signal with an external device, wherein the pad electrode is disposed such that light from one or more transistors residing in the second semiconductor section is blocked; the pad electrode is electrically connected to the first conductive material and to the second conductive material ; and either: the second wiring layer faces the third wiring layer and the pad electrode is formed in the first wiring layer of the first semiconductor section, or the second wiring layer faces the first wiring layer and the pad electrode is formed in the second wiring layer of the second semiconductor section. the second wiring layer faces the third wiring layer and the pad electrode is formed in the first wiring layer of the first semiconductor section, or the second wiring layer faces the first wiring layer and the pad electrode is formed in the second wiring layer of the second semiconductor section. <EOS>