The design, fabrication and experimental investigation of 22-25 MHz fragmented-membrane MEM bulk lateral resonators (BLR) with 100 nm air-gaps on thin (1 and 6 [mu]m) silicon-on-insulator (SOI) are reported. Quality factors as high as 120,000 and motional resistances of as little as 60 k[Omega] are measured under vacuum at room temperature, with 12 V DC bias and low AC power. The temperature influence on the resonance frequency and quality factor is studied and discussed between 80 K and 320 K. Significant quality factor increase and motional resistance reduction are reported at cryogenic temperature. The paper shows that high-quality factor MEM resonators can be integrated on partially depleted thin SOI, which can be a substrate of choice for the fabrication of future integrated hybrid MEMS-CMOS integrated circuits for communication applications.