The invention provides a semiconductor device with high reliability and smaller size and a method of manufacturing the same. A light emitting element as a device element is formed on the front surface of a semiconductor substrate, for example. In detail, an N-type semiconductor layer, a P-type semiconductor layer and pad electrodes are formed on the front surface of the semiconductor substrate. A device element receiving light from the light emitting element (e.g. a photodiode element), for example, and pad electrodes are formed on the front surface of another semiconductor substrate. The semiconductor substrates are attached and integrated with an adhesive layer being interposed therebetween. Wiring layers electrically connected to the pad electrodes and wiring layers electrically connected to the other pad electrodes are formed on the side surface of the semiconductor substrate.