The present invention provides a highly controllable device for exposure from the back side and an exposure method, and also provides a method of manufacturing a semiconductor device using the same. The present invention involves exposure with the use of the back side exposure device of which a reflecting means is disposed on the front side of a substrate, apart from a photosensitive thin film surface by a distance X(X=0.1 m to 1000 m), and formation of a photosensitive thin film pattern in a self alignment manner, with good controllability, at a position a distance Y away from the end of a pattern. The invention fabricates a TFT using that method.