A semiconductor device and a method of fabricating thereof, including preparing a substrate including a first and second region; forming first and second conductive lines on the first and second region, respectively, the first conductive lines being spaced apart at a first interval and the second conductive lines being spaced apart at a second interval wider than the first interval; forming a dielectric layer in spaces between the first and second conductive lines; etching the dielectric layer until a top surface thereof is lower than top surfaces of the first conductive lines and the second conductive lines; forming a spacer on the etched dielectric layer such that the spacer covers an entire top surface of the etched dielectric layer between the first conductive lines and exposes portions of the etched dielectric layer between the second conductive lines; and removing portions of the etched dielectric layer between the second conductive lines.