Let f(x,y) be a word of
length greater than 2 starting in y and ending in x. The purpose of this paper is to
prove that a semigroup satisfies an identity xy = f(x,y) if and only if it is
an inflation of a semilattice of groups satisfying the same identity. As its
consequence we find a necessary and sufficient condition for xy = f(x,y) to imply
commutativity.