| abstract |
A transistor including an oxide semiconductor film with extremely low off-state current is provided. Further, by using the transistor, a semiconductor device with extremely low power consumption is provided. A base insulating film from which oxygen is released by heat treatment is formed over a substrate, a first oxide semiconductor film is formed over the base insulating film, and the substrate is heat treated. Next, a conductive film is formed over the first oxide semiconductor film, and the conductive film is processed to form a source electrode and a drain electrode. Next, a gate insulating film that covers the source electrode, the drain electrode, and the second oxide semiconductor film is formed immediately after the first oxide semiconductor film is processed to form the second oxide semiconductor film, and the gate insulating film is formed. A gate electrode is formed on the film. [Selection] Figure 1 |