We report experiments to determine whether the room temperature one-dimensional conductance quantization (1DCQ) is present at the V∣amorphous-V2O5 interphase in as-deposited V∣amorphous-V2O5∣V devices, or nucleated by a critical event at the threshold voltage VT where ballistic transport was initiated. The fit of the material parameters (barrier width, barrier height, dielectric constant) to the I–V data, the oxide thickness independence of resistance, and variations in the device capacitance with junction area and oxide thickness, suggest that the 1DCQ is associated with the formation of a low dimensional conducting filament through a ∼ 20 Å-thick VOx interphase layer. The data show that VT is unusually low ( ∼ 8 kT/q where T = 300 °K), nearly independent of device area and oxide thickness, and has only a small ( ∼ kT/q) statistical variation from device to device. These data suggest that the interphase transition at the voltage VT is reversible, but, were inconclusive in determining whether the interphase transition occurs at a critical field or is induced by thermal effects. The threshold voltage VT also decreases as (T−Tc)n (n ∼ 0.5) going to zero near Tc ≈ 60 °C. An analysis of the data suggests that the interphase transition most likely occurs by a critical event associated with an inelastic transfer of energy ∼ kTc/q at the V∣a-V2O5 interphase. © 1997 American Institute of Physics.