Field effect transistor and method for manufacturing the same

A method for manufacturing a field effect transistor, comprising:

• forming a mask comprising an insulating film on a semiconductor layer containing Si, the semiconductor layer being formed on a semiconductor substrate;
• forming the semiconductor layer into a mesa structure by performing etching with the use of the mask, the mesa structure having a pair of sidewalls extending in a first direction parallel to an upper face of the semiconductor substrate, the sidewalls facing each other;
• reducing a distance between the sidewalls to be less than a width of the mask in a second direction perpendicular to the first direction and flattening the sidewalls by performing a heat treatment in a hydrogen atmosphere, the flattened sidewalls being formed with one of a {110} plane or a {111} plane;
• forming a gate insulating film covering the flattened sidewalls;
• forming a gate electrode covering the gate insulating film;
• and
• forming source and drain regions at portions of the mesa structure, the portions being located on two sides of the gate electrode.