This paper presents a 120 GHz low-power down converter in a 65 nm complementary metal-oxide-semiconductor (CMOS) process for chip to chip communication. The center frequency of the down converter is 120 GHz. The proposed down converter consists of an active balun, a down conversion mixer, and a baseband amplifier. The average insertion loss of the active balun was 1 dB within a 3 dB bandwidth. The down conversion mixer achieved a conversion gain of -13 dB with a local oscillator (LO) power of as small as -10 dBm. The peak gain of the baseband amplifier was 28.3 dB with a 3 dB bandwidth of 7.7 GHz. This down converter achieves a high conversion gain of 14.3 dB with an LO power of -10.6 dBm. The proposed down converter consumes 25 mW and has a chip size of 0.89 mm(2).