A semiconductor device includes a source region and a drain region of a first conductivity type, a body region of a second conductivity type between the source region and the drain region, a gate configured to control current through a channel of the body region, a drift zone of the first conductivity type between the body region and the drain region, a superjunction structure formed by a plurality of regions of the second conductivity type laterally spaced apart from one another by intervening regions of the drift zone, and a diffusion barrier structure disposed along sidewalls of the regions of the second conductivity type of the superjunction structure. The diffusion barrier structure includes alternating layers of Si and oxygen-doped Si and a Si capping layer on the alternating layers of Si and oxygen-doped Si.