Let ${\cal S}$ be a locally compact semigroup and $M_a({\cal S})$
be its semigroup algebra. In this paper, we investigate inner
invariant means on $L^\infty({\cal S},M_a({\cal S}))$ of all $M_a(
{\cal S})$-measurable complex-valued bounded functions on ${\cal
S}$ and its closed subspace $C_b({\cal S})$, the space of all
bounded continuous complex-valued functions on ${\cal S}$. We also
study topological inner invariant means on certain closed
subspaces $X$ of $L^\infty({\cal S},M_a({\cal S}))$ and their
relation with inner invariant means on $X$.