Contamination of an interface of respective films constituting a TFT due to an contaminant impurity in a clean room atmosphere becomes a great factor to lower the reliability of the TFT. Besides, when an impurity is added to a crystalline semiconductor film, its crystal structure is broken. By using an apparatus for manufacturing a semiconductor device including a plurality of treatment chambers, a treatment can be made without being exposed to a clean room atmosphere in an interval between respective treatment steps, and it becomes possible to keep the interface of the respective films constituting the TFT clean. Besides, by carrying out crystallization after an impurity is added to an amorphous semiconductor film, the breakdown of the crystal structure of the crystalline semiconductor film is prevented.