This paper proposes a MEMS relay circuit by paralleling an auxiliary MOSFET with a MEMS switch. During the turn-on and turn-off transition, MOSFET is turned on at first to guarantee the switching voltage of MEMS switch is almost zero; for normal switch-on condition the MEMS switch with low on-resistance is turned on and the MOSFET is turned off. To meet the requirement of isolation between control side and power side, a transformer is designed in the control circuit and this single transformer achieves both power transfer and on- off control signal transfer. Thus the size of MEMS relay is reduced. Finally, a prototype was built and it validates the design of MEMS relay structure and single transformer circuit. Superior switching performance, fast response, low on-resistance and small size are achieved by the MEMS relay.