An object is to provide a semiconductor device provided with a thin film transistor having excellent electric characteristics using an oxide semiconductor layer. An In—Sn—O-based oxide semiconductor layer including SiOX is used for a channel formation region. In order to reduce contact resistance between the In—Sn—O-based oxide semiconductor layer including SiOX and a wiring layer formed from a metal material having low electric resistance, a source region or drain region is formed between a source electrode layer or drain electrode layer and the In—Sn—O-based oxide semiconductor layer including SiOX. The source region or drain region and a pixel region are formed using an In—Sn—O-based oxide semiconductor layer which does not include SiOX.