A high performance circuit is formed by using a TFT with less fluctuation in characteristics, and a semiconductor device including such a circuit is formed. When the TFT is formed, first, a base film and a semiconductor film are continuously formed on a quartz substrate without exposing to the air. After the semiconductor film is crystallized by using a catalytic element, the catalytic element is removed. In the TFT formed in such a process, fluctuation in electrical characteristics such as a threshold voltage and a subthreshold coefficient is extremely small. Thus, it is possible to form a circuit, such as a differential amplifier circuit, which is apt to receive an influence of characteristic fluctuation of a TFT.