Four types of pinned magnetic tunnel junctions (MTJs) with threekeylayer structures of Py/Al2O3/Py,Py/Al2O3/Co,Co/Al2O3/Py,Co/Al2O3/Co were fabricated using a contact shadow mask method and an antiferromagnetically pinned layer of Ir22Mn78.The slit width of the shadow mask is 100μm, and the composition of permalloy is Py＝Ni79Fe21.For example, the MTJs of Co/Al2O3/Co with a tunneling magnetoresistance (TMR) ratio of 17.2%, the junction resistance of 76?Ω, the resistance area product RS of 760?kΩμm2, and the freelayer reversal field of 1114A·m-1 defined as the field where the TMR rises to 50% of the total jump were achieved at the as deposited state at room temperature. Furthermore, when the magnetic field increases from 0 to 1114?A·m-1 the TMR ratio jumps from 0 to 17.2% with one step, which shows that the magnetic field sensitivity of the junction reached at 0.1%/(103A·m-1). While, the TMR vs external filed H curves for the pinned MTJs of Co/Al2O3/Py show a good rectangular shape with a small free-layer reversal filed of 1114?A·m-1. Our exprimental results show that such MTJs can be used to fabricate the magnetic field sensitive sensors or prototype demonstration devices of magnetoresistive random access memory.