A semiconductor device includes: a substrate including a first region and a second region; a first gate stack on the first region of the substrate; a first source/drain contact at a first side of the first gate stack, wherein the first source/drain contact is connected to the substrate; a second gate stack on the second region of the substrate; and a second source/drain contact at a first side of the second gate stack, wherein the second source/drain contact is connected to the substrate, wherein a height of the second source/drain contact is greater than a height of the first source/drain contact, and wherein a width of the second source/drain contact is greater than a width of the first source/drain contact.