The present invention discloses an over-current protection device comprising two metal foils and a positive temperature coefficient (PTC) material layer. The PTC material layer is sandwiched between the two metal foils and contains at least one crystalline polymer, a non-oxide electrically conductive ceramic powder and a non-conductive filler. The non-oxide electrically conductive ceramic powder exhibits a certain particle size distribution. The PTC material layer presents resistivity below 0.1 Ω-cm.