Low applied voltage in electrowetting-on-dielectric (EWOD) can be achieved using thin dielectric. However it is followed by high possibility of dielectric failure. On the other hand, multi-layer dielectric has been known as a way to enhance the dielectric reliability by delaying the dielectric breakdown. In this paper, we report a modified structure of multi-layer insulator called sandwich-like multi-layer structure. This structure is built by dividing one layer into two sections and inserting the other layer between them, resulting a stack with an additional layer but identical in thickness with the conventional multi-layer structure. Using Parylene C and Aluminum Oxide (Al2O3), sandwich-like multi-layer structure shows an improvement in dielectric reliability by delaying the occurrence of dielectric breakdown without sacrificing the operational voltage. Dielectric breakdown is investigated by observing the bubbles forming during electrowetting test caused by electrolysis.