Semiconductor device with increased channel length and width and method for manufacturing the same

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

• forming an isolation layer in the semiconductor substrate to define an active region that includes a channel portion;
• first etching the channel portion in the active region;
• forming a spacer over a side wall of the isolation layer exposed by the first etching of the channel portion in the active region and a side wall of the first etched channel portion;
• second etching the first etched channel portion, except the edges in a direction of the channel width thereof and the portion of the active region that is not first etched using the spacer as an etching mask so that a U-shape groove is formed in the channel portion of the active region and the entire active region is placed below a upper surface of the isolation layer;
• removing the spacer;
• and
• forming a gate over the channel portion in the active region including the U-shape groove.