Methods of rectifying a sidewall profile of a fin-shaped stack structure are provided. An example method includes forming, on a substrate, a first fin-shaped structure and a second fin-shaped structure each including a plurality of channel layers interleaved by a plurality of sacrificial layers; depositing a first silicon liner over the first fin-shaped structure and the second fin-shaped structure; depositing a dielectric layer over the substrate, the first fin-shaped structure and the second fin-shaped structure; etching back the dielectric layer to form an isolation feature between the first fin-shaped structure and the second fin-shaped structure and to remove the first silicon liner over the first fin-shaped structure and the second fin-shaped structure to expose sidewalls of the plurality of channel layers and the plurality of sacrificial layers, and epitaxially depositing a second silicon liner over the exposed sidewalls of the plurality of channel layers and the plurality of sacrificial layers.