In this paper, we characterize the function space and L1-space of the [topological] Tensor product of [topological] semigroups. As a consequence, for arbitrary [topological] groups G1 and G2, it will be shown that G1×G2 is an extension of G1ÄsG2 by a proper normal subgroup N i,e G1ÄsG2=G1×G2/N