A method of manufacturing a trench oxide in a trench for a gate structure in a semiconductor substrate is described. The method includes: generating the trench in the semiconductor substrate; generating an oxide layer over opposing sidewalls of the trench; damaging at least a portion of the oxide layer by ion implantation; coating the oxide layer with an etching mask; generating at least one opening in the etching mask adjacent to one of the opposing sidewalls; and partly removing the oxide layer by etching the oxide layer beneath the etching mask down to an etching depth at the one of the opposing sidewalls by introducing an etching agent into the opening.