The magnetotransport properties of tunnel junctions with the structure of Ta 5 nm/Cu 20 nm/Ta 5 nm/Ni76Fe24 2 nm/Cu 5 nm/Mn75 Ir25 10 nm/Co71Fe29 4 nm/Al–N/Co71Fe29 4 nm/Ni76Fe2420 nm/Ta 5 nm were investigated. When the Al thickness, nitridation time, and annealing temperature were 1 nm(0.8 nm), 50 s(35 s), and 280 °C(300 °C), tunnel magnetoresistance (TMR) ratio and resistance-area product were 49%(34%) and 3×104 Ω μm2(1.5×104Ωμ m2), respectively. In order to clarify the annealing temperature dependence of TMR ratio, the local transport properties were studied using conducting atomic force microscope for Ta 5 nm/Cu 20 nm/Ta 5 nm/Ni76Fe24 2 nm/Cu 5 nm/Mn75Ir25 10 nm/Co71Fe29 4 nm/Al(0.8 nm)–N junction fabricated with the nitridation time of 35 s and Ar+N2 plasma as a function of annealing temperature. The large TMR at 300 °C, where the TMR ratio of the corresponding magnetic tunnel junction had the maximum value of 34%, could be well elucidated by the enhancement of the average barrier height ϕave, and the reduction of its fluctuation. After annealing at 340 °C, the leakage current was observed and the TMR ratio decreased.