An object of the present invention to provide a semiconductor device manufactured in short time by performing the step of forming the thin film transistor and the step of forming the photoelectric conversion layer in parallel, and to provide a manufacturing process thereof. According to the present invention, a semiconductor device is manufactured in such a way that a thin film transistor is formed over a first substrate, a photoelectric conversion element is formed over a second substrate, and the thin film transistor and the photoelectric conversion element are connected electrically by sandwiching a conductive layer between the first and second substrates opposed to each other so that the thin film transistor and the photoelectric conversion element are located between the first and second substrates. Thus, a method for manufacturing a semiconductor device which suppresses the increase in the number of steps and which increases the throughput can be provided.