Image sensor including first and second overlapping device isolation patterns

An image sensor includes a lower substrate including logic circuits and an upper substrate including pixels. Transistors provided on the upper substrate have the same conductivity type. Each of the transistors includes source/drain regions provided in the upper substrate, an upper gate electrode provided on the upper substrate, and a silicon oxide layer disposed between the upper substrate and the upper gate electrode. The silicon oxide layer is in physical contact with the upper substrate and the upper gate electrode.