A semiconductor integrated circuit which reduces and increase in the level of a harmonic signal of an RF transmission output signal at the time of supplying an RF transmission signal to a bias generation circuit of an antenna switch, including an antenna switch having a bias generation circuit, a transmitter switch, and a receiver switch. The on/off state of a transistor of the transmitter switch coupled between a transmitter port and an I/O port is controlled by a transmit control bias. The on/off state of the transistors of the receiver switch coupled between the I/O port and a receiver port is controlled by a receiver control bias. An RF signal input port of the bias generation circuit is coupled to the transmit port, and a negative DC output bias generated from a DC output port is supplied to a gate control port of transistors of the receiver switch.