A semiconductor device with an asymmetric transistor and a method for fabricating the same are provided. The semiconductor device includes: a substrate having a plurality of first active regions, at least one second active region, and a plurality of device isolation regions; gate patterns formed in a step structure over a border region between individual first active regions and second active region, wherein one side of the individual gate pattern is formed over a portion of the individual first active region, and the other side of the individual gate pattern is formed over a portion of the second active region; spacers formed on lateral walls of the gate patterns; first cell junction regions formed in the first active regions, for connecting to storage nodes; and a second cell junction region formed in the second active region, for connecting to a bit line.