Magnetic tunnel junctions (MTJs) were fabricated using an Al–O insulating layer prepared on an epitaxially grown Ni80Fe20 bottom electrode and on a polycrystalline Ni80Fe20 bottom electrode. Crystallographic orientations and surface morphology of the films were examined using x-ray diffraction and atomic force microscopy, respectively. The MTJ with an epitaxial bottom electrode showed a tunnel magnetoresistance (TMR) ratio of 51% after annealing at 250 °C. This value was about two times larger than that of the MTJ with a polycrystalline bottom electrode (27%). The applied bias voltage dependences of the TMR ratios were also much different. The Vhalf values of epitaxial and polycrystalline samples were about 750 and 400 mV, respectively. © 2003 American Institute of Physics.