The inventive concept provides semiconductor devices having through-vias and methods for fabricating the same. The method may include forming a via-hole opened toward a top surface of a substrate and partially penetrating the substrate, forming a via-insulating layer having a first thickness on a bottom surface of the via-hole and a second thickness smaller than the first thickness on an inner sidewall of the via-hole, forming a through-via in the via-hole which the via-insulating layer is formed in, and recessing a bottom surface of the substrate to expose the through-via. Forming the via-insulating layer may include forming a flowable layer on the substrate, and converting the flowable layer into a first flowable chemical vapor deposition layer having the first thickness on the bottom surface of the via-hole.