Embodiments of transistors comprise a gate stack overlying a semiconductor material. The gate stack comprises a deposited oxide layer overlying the semiconductor material, an oxygen-diffusion barrier layer overlying the deposited oxide layer, a high-k dielectric layer overlying the oxygen-diffusion barrier layer, and a conductive material (e.g., an oxygen-gettering conductive material) overlying the high-k dielectric layer. When the conductive material is an oxygen-gettering conductive material, the oxygen-diffusion barrier layer prevents diffusion of oxygen from the deposited oxide layer to the oxygen-gettering conductive material.