An integrated semiconductor mixer includes a substrate (10), a radio-frequency balun (12) disposed on the substrate (10), a local oscillator balun (14) disposed on the substrate (10), an intermediate-frequency port (16) disposed on the substrate (10), and a mixer diode array (18), disposed on the substrate (10), that communicates with the radio-frequency balun (12), the local oscillator balun (14), and the intermediate-frequency port (16), in which the radio-frequency balun (12) is shielded from the local oscillator balun (14) by plated holes (20).