A semiconductor chip includes a first wireless communication circuit, a second wireless communication circuit, and an auxiliary path. The first wireless communication circuit includes a signal path, wherein the signal path includes a signal node. The second wireless communication circuit includes a mixer and a local oscillator (LO) buffer. The LO buffer is arranged to receive and buffer an LO signal, and is further arranged to provide the LO signal to the mixer. The auxiliary path is arranged to electrically connect the LO buffer to the signal node of the signal path, wherein the LO buffer is reused for a loop-back test function of the first wireless communication circuit through the auxiliary path.