An electrical connector includes a housing, a number of contacts received in the housing and a spacer for holding the contacts. The housing includes a mating portion and a pair of extensions extending from the mating portion. The pair of extensions and the mating portion jointly form a receiving space to receive the spacer. The spacer includes a horizontal portion and a vertical portion perpendicular to the horizontal portion. The horizontal portion defines a slot through which the contacts extend. The vertical portion includes an inner wall, an outer wall and a channel extending through the inner wall and the outer wall. The outer wall defines a recess opening in communication with the channel. When the contacts are associated with the spacer, the contacts are partly exposed to the recess opening via the channel for robust heat dissipation.