High-Q silicon micromachined evanescent-mode resonators for K and Ka-band are investigated. Such structures can be realized by loading a below the cut-off waveguide cavity with capacitive posts and can easily be combined to form multi-pole filters. The capacitive post placed inside the cavity lowers its resonant frequency. Therefore, compared to a resonant cavity, the size of the evanescent cavity is dramatically reduced, while still achieving the same resonant frequency. The loss also increases, but relatively high unloaded quality factor can be maintained. Design methods with full-wave analysis and circuit-modeling results are presented. Experimental results for K and Ka-band resonators are also presented.