A technique is proposed to employ the phase shifting capability of a MEMS resonator to form the basic component of a switchless quadrature phase shift keying (QPSK) scheme. The advantages of such an approach include direct baseband to RF modulation, no generation of intermodulation products since the resonator is operated linearly, and small size, cost, and power dissipation. An example phase modulator system built using a 100 MHz SiBAR demonstrates at least 54° of relative phase shift.