A semiconductor device includes a substrate, a plurality of first conductive patterns disposed on the substrate and a plurality of second conductive patterns disposed on the first conductive patterns. Respective air gaps are disposed between adjacent ones of the first conductive patterns overlying a first region of the substrate, while adjacent ones of the first conductive patterns overlying a second region of the substrate do not have air gaps disposed therebetween. The air gaps may include first air gaps, and the device may further include second air gaps disposed between adjacent ones of the second conductive patterns in the second region. Adjacent ones of the second conductive patterns overlying a second region of the substrate may not have air gaps disposed therebetween.