We demonstrate the fabrication and operation of high aspect ratio tensile stressed silicon nitride string resonators. We explore the parameter space of small cross sections, on the order of 100 nm, and long lengths up to 325 μm, demonstrating that such high aspect ratio resonators can be made with standard wet release processing using a material with internal tensile stress. Room temperature quality factors exceed one million at frequencies above 1 MHz. The utility of such high quality factor flexural resonators to probe the interaction of high frequency nanoscale devices with rarefied gases is demonstrated. © 2008 American Institute of Physics.