In addition to the network structures, bulk As2S3 glass contains a small amount of various cage-like molecular inclusions. In contrast, the As4S4 and As4S5 cage-like molecules make up the majority of the structures in As-S thin films freshly prepared by thermal evaporation of the glass. Thermal annealing or white light irradiation of these films leads to polymerization of the molecular cages and formation of a structure similar to that of the bulk material. However, the near-band gap laser irradiation of As-S films results in structural rearrangements of the As4S4 isomer (realgar-to-pararealgar transition). This transformation is reversible during “laser irradiation”—“thermal annealing” cycles. It was found that As-S crystallites can be grown using thermally activated and gold nanoparticle-assisted synthesis. Moreover, under specific synthesis conditions, selective growth of crystallites consisting solely of photosensitive As4S4 or As4S5 cage-like molecules can be achieved. The structure of various As-S crystallites was examined using Raman spectroscopy and density functional theory calculations. The selective growth of microcrystallites and their laser-induced transformation are discussed in detail.