A semiconductor device includes a silicon substrate; a device isolation structure formed in the silicon substrate to delimit an active region which has a pair of gate forming areas, a drain forming area between the gate forming areas, and source forming areas outside the gate forming areas; an asymmetric bulb-type recess gate formed in each gate forming area of the active region and having the shape of a bulb on the lower end portion of the sidewall thereof facing the source forming area; and source and drain areas respectively formed on the surface of the substrate on both sides of the asymmetric bulb-type recess gate.