The non-leptonic $B^0_s \rightarrow D_s^{\pm} K^{\mp}$ decays, which occur via pure tree diagrams, allow a theoretically clean determination of the CKM angle $\gamma$. Considering recent LHCb results, and combining them with data for $B_s \rightarrow D^{\mp} \pi^{\pm}$ modes, our goal is to shed more light on the resolution of the ambiguities in the extraction of gamma of the unitarity triangle as well as to explore possible New Physics effects. The