  We have observed that submicron sized Al--AlO{$_x$}--Al tunnel junctions can
be stabilized completely by annealing them in vacuum at temperatures between
$350^{\circ}$C and $450^{\circ}$C. In addition, low temperature
characterization of the samples after the annealing treatment showed a marked
improvement of the tunneling characteristics due to disappearance of unwanted
resonances in the current. Charging energy, tunneling resistance, barrier
thickness and height all increase after the treatment. The superconducting gap
is not affected, but supercurrent is reduced in accordance with the increase of
tunneling resistance.
