The aim of the present paper is to study half-lightlike submanifolds of a semi-Riemannian manifold endowed with a metallic structure. We introduce a special half-lightlike submanifold called screen semi-invariant half lightlike submanifold in metallic semi-Riemannian manifolds and give an example. We present necessary and sufficient conditions for the distributions included in the definition of such half lightlike submanifolds to be integrable. Moreover, we analyze geometry of a screen semi-invariant half lightlike submanifold in a locally metallic semi- Riemannian manifold when it is totally geodesic and screen conformal.