For future implementation of ferromagnetic tunnel junctions, we need a better understanding of the influence of the insulating barrier preparation method on the junction resistance, tunnel magnetoresistance (TMR), and its voltage bias dependence. In this letter, we focus on the bias dependence of junctions (Co-Al2O3-Ni80Fe20) prepared by ultraviolet light assisted in situ oxidation in an O-2 ambient. For an initial Al thickness of 1.3 nm, the resistance times area product of the junctions is 60 k Omega mu m(2), while showing up to 20% TMR at 5 mV bias. The decrease of TMR with bias voltage up to 1 V is remarkably small leading to V-1/2, for which half of the low-bias TMR remains, well over 0.6 V. (C) 2000 American Institute of Physics. [S0003-6951(00)02908-9].