In this work, we investigated the electronic structure, and mechanical, transport and optical properties of the van der Waals heterostructure formed from silicane (SiH) and Janus Ga₂SSe monolayers using first-principles prediction. The out-of-plane symmetry in the Janus Ga₂SSe monolayer leads to the formation of two different types of Ga₂SSe/SiH heterostructure, namely SGa₂Se/SiH and SeGa₂S/SiH stacking patterns. All stacking patterns of the SiH/Ga₂SSe heterostructure are thermodynamically, mechanically and energetically stable at room temperature. Furthermore, the generation of the SiH/Ga₂SSe heterostructure gives rise to a reduction in the band gap, demonstrating that the electrons move faster from the valence bands to the conduction bands. The SiH/Ga₂SSe heterostructure is a semiconductor with a direct band gap of about 0.68 or 0.95 eV, depending on the stacking pattern. The SiH/Ga₂SSe heterostructure forms type-II band alignment for all stacking patterns, indicating that the photogenerated carriers are separated effectively, thus enhancing the photocatalytic performance. Moreover, the carrier mobilities for electrons and holes of the Ga₂SSe/SiH heterostructure are higher than those of the constituent SiH and Ga₂SSe monolayers in both the x and y directions, suggesting that the performances of electronic devices based on the Ga₂SSe/SiH heterostructure would be excellent and reliable. The formation of the Ga₂SSe/SiH heterostructure also gives rise to an enhancement of the absorption coefficient in both the visible and ultraviolet regions. Our findings could give valuable guidance for the design of high-efficiency devices based on the SiH/Ga₂SSe heterostructure.