An over-current protection device comprises two metal foils, a positive temperature coefficient (PTC) material layer and a packaging material layer. The PTC material layer is sandwiched between the two metal foils and has a volume resistivity below 0.1 Ω-cm. The PTC material layer includes (i) plural crystalline polymers having at least one crystalline polymer with a melting point less than 115° C.; (ii) an electrically conductive nickel filler having a volume resistivity less than 500 μΩ-cm; and (iii) a non-conductive metal nitride filler. The electrically conductive nickel filler and non-conductive metal nitride filler are dispersed in the crystalline polymer. The packaging material layer which encapsulates the chip is essentially comprised of the PTC layer and the two metal foils. The packaging material layer is formed by reacting epoxy resin with a hardener having amide functional group.