Reliability of BST (Ba 0.7 Sr 0.3 TiO 3 ) capacitors made by using a MOD technique was studied in terms of TDDB. DLTS analysis revealed peak-shift toward the lower-temperature side as the degradation goes further. Obtained energy level of interfacial states at grain boundaries was 0.75eV. We found the capture cross section of the level increases after the bias-temperature stress. We also found that the larger grain size of BST film gives longer lifetime. These results suggest that the reliability is to be determined by the interface of grains.