An electrical connector includes an insulative housing and a plurality of signal and ground contacts retained in the housing. The housing forms opposite mating surface and mounting surface, and a plurality of signal contact passageways and ground contact passageways extending therethrough to receive the signal contacts and ground contacts therein. All the mating surface, the mounting surface and the set of interior surfaces of each signal contact passageway and each ground contact passageway are plated/coated with corresponding metal layers while some dividing structures are formed on the mating surface and the mounting surface so as to electrically separate the metal layers of the signal contact passageways from those of the ground contact passageways.