An electrical connector includes an insulative housing and a plurality of contacts retained within the housing as a contact module. The housing includes a base and a mating tongue forwardly extending from the base. The contacts are arranged with two rows contacting sections respectively exposed upon two opposite surfaces of the mating tongue, and one row mounting sections for mounting to a same plane of a printed circuit board. Each contact has a linking section between the contacting section and the mounting section. The contacts are grouped by one grounding contact associated with a pair of neighboring differential pair signal contacts in an isosceles triangular configuration wherein the grounding contact is located at the top apex. The linking section of grounding contact of the outermost group is widened compared with those of the remaining contacts for lowering the corresponding impedance.