A millimeter-wave transistor device includes a plurality of sub-cells arranged in matrix array, each of the sub-cells having a longitudinal gate finger elongating along a reference y-axis, a source doping region disposed at one side of the longitudinal gate finger and a drain doping region at the other side of the longitudinal gate finger opposite to the source doping region; and at least three parallel connecting bars extending along a reference x-axis, electrically connecting with respective distal ends of the longitudinal gate finger of each of the sub-cells.