To provide a semiconductor device and a process for manufacturing the same which is capable of suppressing short channel effect and preventing a current from leaking between a contact and a silicon substrate. The semiconductor device of the present invention comprises a silicon substrate on which a source/drain area (3 in FIG. 1), a silicon oxide layer (4 in FIG. 1) and a silicon nitride layer (5 in FIG. 1) are successively formed in this order, and a trench which extend through said layers to split the source/drain area. A columnar gate electrode (9 in FIG. 1) is formed within the trench in such a manner that it is spaced from the inner wall of the trench and a lightly doped drain (LDD) area (10 in FIG. 1) is formed at an area of the bottom of the trench in which no gate electrode is disposed. In such a structure, the short channel effect which occurs in association with reduction in the gate length is suppressed.