AbstractA high‐frequency switch utilizing a GaAs FET as an analog switch is expected to operate in a broad band and can be integrated in a monolithic IC form. Since only a single power supply is needed for the gate bias and the power consumption of the switch can be made zero, it is useful in the area where a small size and low power consumption are required. To investigate the feasibility of a broadband GaAs monolithic switch, this paper first derives an equivalent circuit of the switch from the structural model of the FET and the relation between the switch characteristics and the device parameters of the FET. The design method of the switch is then developed. Next, the monolithic switches of SPDT and DPDT structures are fabricated by ion‐implantation technology and their characteristics are evaluated so that the validity of the equivalent circuit model is confirmed. The GaAs monolithic SPDT switch realized has the passband of dc to 3.3 GHz, insertion loss less than 0.7 dB (dc to 2 GHz), isolation more than 20 dB, switching time 2 ns and the maximum distortionless signal input power 20 dBm. Similarly, good performance has been obtained for the DPDT switch.