A semiconductor device includes a semiconductor substrate having an active region including a channel portion. An isolation layer is formed in the semiconductor substrate to define the active region, and a gate is formed over the channel portion in the active region. The active region of the semiconductor substrate is etched to such that the entire active region is below an upper surface of the isolation layer. A U-shaped groove is formed in the channel portion of the active region, except the edges in a direction of the channel width thereof, in order to increase the channel width. In the semiconductor device, there is an increase in channel length and channel width leading to a reduction in leakage current and on increase in operation current.