  We report on combined measurements of heat and charge transport through a
single-electron transistor. The device acts as a heat switch actuated by the
voltage applied on the gate. The Wiedemann-Franz law for the ratio of heat and
charge conductances is found to be systematically violated away from the charge
degeneracy points. The observed deviation agrees well with the theoretical
expectation. With large temperature drop between the source and drain, the heat
current away from degeneracy deviates from the standard quadratic dependence in
the two temperatures.
