The present invention relates to an optical transceiver that installs an optical transmitting assembly and an optical receiving assembly both are compact, inexpensive, and capable of operating at a high speed. The optical transmitting assembly of the present invention provides the metal bottom that installs the thermoelectric cooler thereon and the semiconductor optical device is mounted, via the insulating substrate, on the thermoelectric cooler. The first and second multi-layered ceramic substrates are provided to surround the thermoelectric cooler. The DC signal or the low-frequency signal for the thermoelectric cooler and the semiconductor optical device is supplied through the first ceramic substrate, while the high frequency signal for the semiconductor device, with the complementary signal having the opposite phase to the high frequency signal, is provided to the semiconductor device through the inner layer of the second ceramic substrate and the insulating substrate. The semiconductor light-receiving device, which monitors light emitted from the semiconductor light-emitting device, is mounted on the top layer of the second ceramic substrate. Thus, the transmission path for the high frequency signal from the drive circuit installed outside of the transmitting assembly to the light-emitting device becomes substantially linear.