We have measured the avalanche breakdown voltage (Vb) in GaAsp‐i‐ndiodes as a function of hydrostatic pressure up to 14 kbar. The pressure coefficient ofVbwas small and opposite in sign compared to that of the band gap. A lucky‐drift calculation ofVbincluding the effects of pressure on both the phonon scattering and ionization rates showed that the ionization threshold energy does not scale with the band gap. Instead, the effective threshold scales with an average of the energies of the &Ggr;,X, andLconduction‐band minima. This is direct evidence that pair production yields final electron states distributed between conduction‐band valleys. ©1995 American Institute of Physics.