This paper presents a monolithic 0.8-to-18GHz reconfigurable transceiver with dual-mode of direction and conversion functions. In the direction mode, the transceiver processes the signals from 0.8 to 5GHz. While in the conversion mode, it up-converts or down-converts the signals in a frequency from 4.5 to 18GHz. An overlap of 0.5GHz exists in the two modes, so that the transceiver will be flexible in frequencies from 4.5 to 5GHz. In the RX, the two modes share the LNA, tunable LPF, and VGA. Similarly, the two modes of TX share the VGA and reconfigurable PA. The proposed transceiver was prototyped using a 0.15-µm E-mode GaAs pHEMT process. The RX exhibits gain range of 7.3 to 41.9dB, gain step of 1dB, tunable instantaneous bandwidth from 1 to 4.2GHz. The TX demonstrates gain ranging from -2.1 to 30.4dB and output 1dB compression point of 18.8dBm. The chip occupies 79.8-mm 2 area including padframe.