  We propose a remarkably simple electronic refrigerator based on the Coulomb
barrier for single-electron tunneling. A fully normal single-electron
transistor is voltage $V$ biased at a gate position such that tunneling through
one of the junctions costs an energy of about $k_BT \ll eV, E_C$, where $T$ is
the temperature and $E_C$ is the transistor charging energy. The tunneling in
the junction with positive energy cost cools both the electrodes attached to
it. Immediate practical realizations of such a refrigerator make use of Andreev
mirrors which suppress heat current while maintaining full electric contact.
