  We investigate electronic distributions in nonequilibrium tunnel junctions
subject to a high voltage bias $V$ under competing electron-electron and
electron-phonon relaxation processes. We derive conditions for reaching
quasi-equilibrium and show that, though the distribution can still be thermal
for low energies where the rate of the electron-electron relaxation exceeds
significantly the electron-phonon relaxation rate, it develops a power-law tail
at energies of order of $eV$. In a general case of comparable electron-electron
and electron-phonon relaxation rates, this tail leads to emission of
high-energy phonons which carry away most of the energy pumped in by the
injected current.
