A test head assembly for a semiconductor device has a carrier, a pin seat and a test wire assembly. The carrier is formed in an L shape and has a lateral board, a perpendicular board and a opening formed through the perpendicular board. The pin seat is mounted in the corresponding opening. The test wire assembly has a test head, a plurality of connectors and a plurality of test wires. The test head is mounted on an outer sidewall of the lateral board and connected to the pin seat through the test wires and the connectors. Therefore, the pin seat is mounted on the perpendicular board of the L-shaped uprightly and the test head is mounted on the lateral board. The pin seat and the test head are not parallel to each other, and a lateral size of the test head assembly is reduced to increase the space usage.