Stepped-impedance resonators (SIR) with HEMTs loaded at one end are used to develop a 40 GHz MMIC SPDT filter integrated switch. The HEMTs are used to switch the resonant frequencies of the loaded stepped-impedance resonators. At on-state, the resonators resonate at the same center frequency to pass the RF signal. With the coupled-resonator filter theory, the filter response could be easily designed and synthesized. At off-state, the resonant frequencies of the resonators between input and output ports are staggered to block the RF signal. In this paper, a compact 40-GHz MMIC single-pole-double-throw (SPDT) switch with integrated a third-order bandpass filter is demonstrated. At thru-port, a bandpass filter response with measured insertion loss of 3.1 dB at the center frequency is obtained. At the isolated-port, an isolation of higher than 30 dB is also obtained. The proposed circuit successfully combines an SPDT switch and a bandpass filter into a single circuit component, and makes a high level of MMIC integration become possible.