Microscopical investigation of leakage behaviors of Hf-based high-k gate stacks was achieved by means of electron-beam-induced current (EBIC) method. With this method, we could observe the pre-existing and stress induced defect in high-k. This pre-existing defect affect on MOSFET characteristics. We investigated in detail the relationship between the defect (in bulk high-k and interface) and 1/f noise on (110) and (100) substrates. The 1/f noise is strongly related to the degradation in the hole mobility due to the pre-existing defect or process integration damage. On the other hand, the 1/f noise of nMOSFETs is rerated to interface defects rather than electron mobility degradation.