Unidirectional self-aligned gate endcap (SAGE) architectures with gate-orthogonal walls, and methods of fabricating unidirectional self-aligned gate endcap (SAGE) architectures with gate-orthogonal walls, are described. In an example, integrated circuit structure includes a first semiconductor fin having a cut along a length of the first semiconductor fin. A second semiconductor fin has a cut along a length of the second semiconductor fin. A gate endcap isolation structure is between the first semiconductor fin and the second semiconductor fin. The gate endcap isolation structure has a substantially uniform width along the lengths of the first and second semiconductor fins.