Let M(S) be the
Banach algebra of all bounded regular Borel measures on alocally compact
semigroup S with variation norm and convolution as multiplication and
M0(S) the probability measures in M(S). We obtain necessary and sufficient
conditions for the semigroup S to have the (ergodic) property that for each
ν ∈ M(S),|ν(S)| =inf{∥ν ∗ μ∥ : μ ∈ M0(S)}, an extension of a known result for
locally compact groups.