A semiconductor device with a buried layer has a deep trench structure abutting the buried layer and a self-aligned sinker along sidewalls of the deep trench structure. The semiconductor device may be formed by forming a portion of a deep trench down to the buried layer, and implanting dopants into a substrate of the semiconductor device along sidewalls of the deep trench, and subsequently forming a remainder of the deep trench extending below the buried layer. Alternatively, the semiconductor device may be formed by forming the deep trench to extend below the buried layer, and subsequently implanting dopants into the substrate of the semiconductor device along sidewalls of the deep trench.