A test jig is for testing electrical characteristics of a high frequency semiconductor device in a package having a ground electrode and a high frequency signal electrode. The test jig includes a test circuit substrate with a microstrip line structure, a grounding block and a high frequency signal contact pin. The test circuit substrate includes an insulating substrate, a ground conductor on a bottom surface of the insulating substrate and high frequency signal wiring on a top surface of the insulating substrate. The grounding block is disposed on the top surface of the insulating substrate and connected to the ground conductor. The high frequency signal contact pin is disposed on the top surface of the insulating substrate and connected to the high frequency signal wiring. The high frequency signal contact pin is spaced from the grounding block.