A reversible reduction of breakdown voltage is observed when mechanical stress is applied to siliconp‐njunctions. This effect can best be investigated in junctions exhibiting uniform avalanche breakdown. When uniaxial stress is applied the normalized reduction of breakdown voltage &Dgr;V/VBis proportional to stress, the proportionality constant being of the order of 10−12dyn−1cm2. When stress is applied by means of a flat stylus, &Dgr;V/VBis proportional to the load, when a spherical stylus is used, &Dgr;V/VBis proportional to the cube root of load. It can be shown that the relative current change for a given force is to a first approximation independent of diode area and breakdown voltageVB. It is proposed that the effect is caused by reduction of the energy gap.