A semiconductor device including a buried cell array transistor and an electronic device including the same are provided. The device includes a field region in a substrate and the filed region defines an active region. A first source/drain region and a second source/drain region are in the active region. A gate trench is between the first and second source/drain regions, and in the active region and the field region. A gate structure is within the gate trench. The gate structure includes a gate electrode, an insulating gate capping pattern on the gate electrode, a gate dielectric between the gate electrode and the active region, and an insulating metal-containing material layer between the insulating gate capping pattern and the active region.