In this work, we present the rational synthesis of a novel, highly selective etchant, N-(4-methoxybenzyl)-(pyren-1-yl)amine, enabling the facile and direct fabrication of free-standing 3D structures within an arsenic−sulfide all-inorganic photoresist, patterned via 3D direct laser writing. The chemical and physical underpinnings of this novel wet etchant are described in detail. Our novel molecule enables the fabrication of intricate, shrinkage-free 3D structures with minimum feature sizes of 180 nm in only one etching step. Because of the high transparency of arsenic−sulfide glass in the telecommunication window, structures fabricated along these lines could be well-suited as final structural elements for 3D optical structures and devices in the sub-micrometer scale. The results presented here enable their facile realization, thus making this material a desirable alternative to traditional photopolymers.