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In this paper, we report the design, analysis, fabrication, and characterization of a very high frequency phononic crystal (PnC) micro/nanomechanical resonator architecture based on silicon PnC slab waveguides. The PnC structure completely surrounds the resonant area, and the resonator is excited by a thin aluminum nitride-based piezoelectric transducer stack directly fabricated on top of the resonator. This architecture highly suppresses the support loss of the resonator to the surroundings while providing mechanical support and electrical signal delivery to the resonator. Qs as high as 13 500 in air at a frequency of ~134 MHz with a motional resistance of ~600 Ω and 35-dB spurious-free range of ~20 MHz are obtained. Comparing the Q of this resonator with the previously reported lateral bulk acoustic wave resonators with a similar stack of layers confirms the support loss suppression in this architecture.