Let (S,+) be a commutative
semigroup. If, for each x ∈ S, and for each positive integer n, there exists an (unique)
element y of S such that x = ny, then S is (uniquely) divisible. In this note we
present a more or less intrinsic characterization of uniquely divisible commutative
semigroups and remark on a special sub-class of these semigroups in which it is
possible to discern the fine structure of the addition.