There is provided a semiconductor device including a first gate pattern on a semiconductor substrate, a second gate pattern adjacent to a side surface of the first gate pattern via an ONO film, and an active region located just below the second gate pattern via the ONO film. Here, an element isolation region is formed just below the first gate pattern. In this manner, capacitance between the first gate pattern and the semiconductor substrate and capacitance between the first and second gate patterns are prevented from being measured when measuring capacitance between the second gate pattern which is an upper electrode and the active region which is a lower electrode in order to measure a film thickness of the ONO film just below the second gate pattern.