A method of manufacturing a semiconductor device includes forming a multi-layer stack of alternating first layers of a first semiconductor material and second layers of a second semiconductor material on a semiconductor substrate, forming a first recess through the multi-layer stack, and laterally recessing sidewalls of the second layers of the multi-layer stack. The sidewalls are adjacent to the first recess. The method further includes forming inner spacers with respective seams adjacent to the recessed second layers of the multi-layer stack and performing an anneal treatment on the inner spacers to close the respective seams.