The electrical conductivity of α-Nb2O5 monocrystalline and sintered specimens, measured under a constant ambient oxygen pressure and over the temperature range 300 to 900°C, exhibits an exponential temperature dependence with an activation energy of 1.65 ev. The isothermal conductivity, σ, of near-stoichiometric α-Nb2O5 is related to the ambient oxygen partial pressure, PO2, by the power law expression σ=const PO2—0.24±0.01. Both sets of observations may be rationalized on the basis that slightly-reduced α-Nb2O5 becomes a metal-excess, n-type semiconducting oxide containing oxygen vacancies capable of trapping electrons. A detailed analysis of the relation between conductivity and ambient oxygen pressure has indicated that the conductivity dependency may be ascribed to a mechanism whereby defect levels (due to oxygen ion vacancies with either one or two trapped electrons) are created and electrons are thermally excited from these levels into the conduction band.