Semiconductor device and method for manufacturing the same

A method for manufacturing a semiconductor device comprising the steps of:

• forming a conductive film over a first insulating layer;
• selectively etching the conductive film to form a conductive layer and a first opening penetrating the conductive layer;
• forming a second insulating layer over the conductive layer so that the second insulating layer covers the first opening;
• selectively etching the second insulating layer to form a second opening so as to etch the second insulating layer in the first opening,
• forming a semiconductor layer including a channel formation region of a transistor;
• forming a gate insulating layer over the semiconductor layer;
• and
• forming a gate electrode over the gate insulating layer, the gate electrode overlapping with the semiconductor layer,
• wherein the first opening and the second opening overlap with each other, and
• wherein the conductive layer is one of a source electrode and a drain electrode of the transistor, and the conductive layer is electrically connected to the semiconductor layer.