Abstract: Provided is a semiconductor device and method of making, incorporating a trench having rounded edges. According to an embodiment, a pad oxide layer, nitride layer, and TEOS layer are sequentially formed on a substrate. The TEOS layer, nitride layer, and pad oxide layer are dry-etched using a photosensitive layer pattern as a mask. After removing the photosensitive layer pattern, a trench is formed by dry-etching the substrate using the etched TEOS layer, nitride layer, and pad oxide layer as a mask. A portion of the pad oxide layer is pullback-etched, resulting in a first rounding of the trench. A portion of the etched nitride layer is pullback-etched and a portion of the etched TEOS layer is pullback-etched. The upper corner of the trench of the substrate is dry-etched using the pullback-etched TEOS layer, nitride layer, and pad oxide layer as a mask, resulting in a second rounding of the trench.