| 摘要 |
A transistor including an oxide semiconductor film, in which the threshold voltage is prevented from being a negative value, is provided. A high quality semiconductor device having the transistor including an oxide semiconductor film is provided. A transistor includes an oxide semiconductor film having first to third regions. The top surface of the oxide semiconductor film in the first region is in contact with a source electrode or a drain electrode. The top surface of the oxide semiconductor film in the second region is in contact with a protective insulating film. The thickness of the second region is substantially uniform and smaller than the maximum thickness of the first region. The top surface and a side surface of the oxide semiconductor film in the third region are in contact with the protective insulating film.
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