Semiconductor device and method for manufacturing the same

A method of manufacturing a semiconductor device, the method comprising:

• patterning a semiconductor substrate to form a plurality of active patterns and a first trench between two active patterns adjacent to each other and arranged in a first direction;
• forming a semiconductor layer on the plurality of active patterns to cover the plurality of active patterns such that a thickness of the semiconductor layer along an outer surface of each of the two active patterns diminishes in a downward direction from a top portion toward a bottom portion of each of the two active patterns;
• forming a device isolation layer on the semiconductor layer to cover the semiconductor layer and the plurality of active patterns, fill the first trench, and oxidize at least the semiconductor layer;
• patterning the device isolation layer and the plurality of active patterns to form a second trench intersecting the first trench, and provide the two active patterns protruding from the device isolation layer in the second trench;
• and
• forming gate electrode in the second trench,
• wherein, after the oxidizing the at least the semiconductor layer, substantially all of the semiconductor layer is oxidized at least at a lower part of each of the two active patterns so that a space for a portion of the gate electrode to be filled between the two active patterns is provided in the first trench after the patterning the device isolation layer and the plurality of active patterns.