Micromachined silicon cantilevers have been prepared using anisotropic etching in conjunction with boron doping. They were driven into resonant vibration for periods of over 2000 h and their natural frequencies and quality factors were recorded as a function of aging time. It has been found that aging has occurred in all of the samples tested and this was manifest as an increase in the quality factor and a small decrease in resonant frequency, with both values eventually stabilizing. The magnitude of this effect was found to increase with increasing levels of boron doping within the structures. The mechanism of aging is not clear but may be linked to dislocation damage and activity of interstitial boron with the crystals. ©1995 American Institute of Physics.