A semiconductor device includes a guard active area formed in a substrate, a plurality of transistors disposed in an element area adjacent to the guard active area, each of the transistors including an active area and a gate structure crossing the active area, and a diode transistor disposed between a first transistor and a second transistor among the transistors, and having a diode gate structure connected to the guard active area, a first active area connected to a gate structure of the first transistor, and a second active area connected to a gate structure of the second transistor.