The semiconductor device having a recess channel transistor includes a device isolation structure formed in a semiconductor substrate to define an active region having a recess region at a lower part of sidewalls thereof and a recess channel region formed in the semiconductor substrate under the active region. A method for fabricating the semiconductor device includes forming a device isolation structure in a semiconductor substrate to form an active region having a recess region at a lower part of sidewalls thereof, a gate insulating film formed over the semiconductor substrate including the recess channel region, and a gate electrode formed over the gate insulating film to fill up the recess channel region.