The stacking structure and fabrication process of tunnel junctions were investigated. The stacking structure of the tunnel junctions fabricated was Ta/(Cu,Pt)/Fe20Ni80/IrMn/Co75Fe25/Al- oxide/Co75Fe25/Fe20Ni80/Ta. When the Al thickness, oxidation time, and annealing temperature were 0.8 nm, 15s (10s), and 300°C (250°C), the tunnel magnetoresistance (TMR) ratio and the resistance obtained were 49% (31%) and 1.1 kΩμm2 (230Ωμm2), respectively. In order to investigate the annealing temperature dependence of the TMR ratio, the local electrical properties were measured for a Ta/Fe20Ni80/Pt/Fe20Ni80/IrMn/Co75Fe25/Al- oxide multilayer. The current image became very homogeneous after annealing at around 300°C for 1 h. The increase of the TMR ratio of the junction after annealing can be well explained by taking into account both an increase of barrier height and a decrease of barrier height fluctuation. After further annealing at above 350°C, the barrier height decreased and leakage currents were detected.