A semiconductor device includes: a p-type active region; a gate electrode traversing the active region; an n-type LDD region having a first impurity concentration and formed from a drain side region to a region under the gate electrode; a p-type channel region having a second impurity concentration and formed from a source side region to a region under the gate electrode to form an overlap region with the LDD region under the gate electrode, the channel region being shallower than the LDD region; an n-type source region formed outside the gate electrode; and an n+-type drain region having a third impurity concentration higher than the first impurity concentration formed outside and spaced from the gate electrode, wherein an n-type effective impurity concentration of an intermediate region between the gate electrode and the n+-type drain region is higher than an n-type effective impurity concentration of the overlap region.