We report the temperature-dependent mechanical properties of nanofabricated silicon resonators operating in the megahertz range. Reduction of temperature leads to an increase of the resonant frequencies of up to 6.5%. Quality factors as high as 1000 and 2500 are observed at room temperature in metallized and nonmetallized devices, respectively. Although device metallization increases the overall level of dissipation, internal friction peaks are observed in all devices in the T=160-180 K range. (C) 2000 American Institute of Physics. [S0003-6951(00)01541-2].