Semiconductor device and display device including the semiconductor device

A semiconductor device comprising a transistor,

• wherein the transistor comprises:
• a first oxide semiconductor film over a first insulating film;
• a gate insulating film over the first oxide semiconductor film;
• a second oxide semiconductor film over the gate insulating film;
• and
• a second insulating film over the first oxide semiconductor film and the second oxide semiconductor film,
• wherein the first oxide semiconductor film comprises:
• a channel region overlapping with the second oxide semiconductor film;
• a source region in contact with the second insulating film;
• and
• a drain region in contact with the second insulating film,
• wherein the channel region comprises:
• a first layer;
• a second layer which is in contact with a top surface of the first layer and covers a side surface of the first layer in a channel width direction;
• and
• a third layer in contact with a bottom surface of the first layer, and
• wherein the second oxide semiconductor film has a higher carrier density than the first oxide semiconductor film, and
• wherein the second oxide semiconductor film comprises a plurality of crystals.