Semiconductor device and method for fabricating the same

A method for fabricating a semiconductor device, comprising the steps of:

• stacking a first oxide layer and an oxide semiconductor layer;
• forming a source electrode layer and a drain electrode layer over the first oxide layer and the oxide semiconductor layer;
• stacking an oxide film and a gate insulating film over the source electrode layer and the drain electrode layer;
• forming a gate electrode layer over the oxide film and the gate insulating film;
• forming an oxide insulating layer over the gate insulating film and the gate electrode layer;
• etching the oxide insulating layer to form a sidewall insulating layer in contact with a side surface of the gate electrode layer;
• and
• etching the oxide film and the gate insulating film using the sidewall insulating layer and the gate electrode layer as masks so that a second oxide layer and a gate insulating layer are formed.