SEMICONDUCTOR DEVICE HAVING A LOW-K GATE SIDE INSULATING LAYER

A semiconductor device includes a gate structure crossing an active region of a substrate, and spacers formed on both side surfaces of the gate structure. The gate structure includes an interfacial insulating layer formed on the substrate, a gate dielectric layer formed on the interfacial insulating layer, a gate barrier layer and gate side insulating layers formed on the gate dielectric layer, and a gate electrode on the gate barrier layer. The gate dielectric layer is in contact with inner side surfaces of the spacers, and has a U-shaped longitudinal cross-sectional shape to surround a lower surface and some portions of side surfaces of the gate barrier layer. The gate side insulating layers surround outer side surfaces of the gate barrier layer.