We have proposed novel quad-interface magnetic tunnel junction (MTJ) technology which brings forth an increase of both thermal stability factor $\Delta$ and switching efficiency $\Delta/I_{\text{C}0}$ by a factor of 1.5-2 compared with conventional double-interface MTJ technology. We successfully fabricated the quad-interface MTJ using 300mm process based on novel low damage integration process including PVD, RIE and so on [1]. By developing the quad-interface MTJ, we have achieved about two times larger $\Delta$ and $\Delta/I_{\text{C}0}$. Moreover, we have achieved about two times larger TMR ratio/RA by the stack development specific for the quad-interface MTJ technology. The developed quad-interface MTJ technology regarded as post-double-interface MTJ technology will become an essential technology for the scaling of the STT-MRAM beyond 20nm.