A magnetic tunnel junction (MTJ) device consisting of an ultra-thin insulating layer (called a tunneling barrier) sandwiched by two ferromagnetic electrodes is the key to developing nonvolatile memory, MRAM (magnetoresistive random access memory). In the conventional type of MTJ devices, which use amorphous Al-O as the tunneling barrier, the fact that magnetoresistance is only about 70% at room temperature is an obstacle to large capacity MRAM. We developed a new type of MTJ devices using a tunneling barrier of high quality MgO and achieved a huge magnetoresistance ratio of 230% at room temperature. This is the world's highest performance in a MTJ device, at more than 3 times the level in conventional devices (see Fig. 1).