Abstract. A classical theorem of Burnside asserts that if % is a faithful complex character for the finite group G , then every irreducible character of G is a constituent of some power x" of X ■ Fifty years after this appeared, Steinberg generalized it to a result on semigroup algebras K[G] with K an arbitrary field and with G a semigroup, finite or infinite. Five years later, Rieffel showed that the theorem really concerns bialgebras and Hopf algebras. In this note, we simplify and amplify the latter work.Let K be a field and let A be a .£-algebra. A map A: A -► A ® A is said to be a comultiplication on A if A is a coassociative A^-algebra homomorphism. For convenience, we call such a pair (A, A) a b-algebra. Admittedly, this is rather nonstandard notation. One is usually concerned with bialgebras, that is, algebras which are endowed with both a comultiplication A and a counit e:A -* K. However, semigroup algebras are not bialgebras in general, and the counit rarely comes into play here. Thus it is useful to have a name for this simpler object. Proof. Certainly / is an ideal of A . Now let X = ®J2V€Sr V he the direct sum of the modules in y. Then X is an ,4-module and ann^ X = f)Ve^-aaaA V =