We present a technique for micromachining silicon cantilever beams for thin-him stress measurement. The silicon microbeams were fabricated using a two-step etch process with potassium hydroxide (KOH) as the anisotropic etchant. The final beam geometry is optimized by using a 45% KOH solution and double-side polished silicon wafers as the starting material. We demonstrate a cleaning procedure that produces clean microbeam surfaces as verified by Auger electron spectroscopy. The effects of KOH concentration and temperature on the etch rate, etch rate sensitivity, and silicon surface roughness is discussed. We present results of compressive stress in boron nitride films grown by an ion-assisted process.