A diffusion barrier layer is incorporated between a top semiconductor layer and buried oxide layer. The diffusion barrier layer blocks diffusion of dopants into or out of buried oxide layer. The diffusion barrier layer may comprise a dielectric material such as silicon oxynitride or a high-k gate dielectric material. Alternately, the diffusion barrier layer may comprise a semiconductor material such as SiC. Such materials provide less charge trapping than a silicon nitride layer, which causes a high level of interface trap density and charge in the buried oxide layer. Thus, diffusion of dopants from and into semiconductor devices through the buried oxide layer is suppressed by the diffusion barrier layer without inducing a high interface trap density or charge in the buried oxide layer.