## Compute $H^1(S,\underline{\text{Hom}}(A,\mathbb G_m))$ for a semi-abelian scheme $A$

How can I compute $$H^1(S,\underline{\text{Hom}}(A,\mathbb G_m))$$ (where $$A$$ denotes a semi-abelian scheme over $$S$$, $$\mathbb G_m$$ denotes the multiplicative group over $$S$$ and $$\underline{\text{Hom}}$$ denotes the Hom sheaf)?