This Letter reports avalanche noise studies on microplasma‐free guard‐ring avalanche diodes. The low and high frequency approximations of Hines' theory are compared with experimental results at 1 kHz and 3 to 9 GHz, respectively. Good agreement is found between experiment and theory at both low and high frequencies. The open‐circuit spectral voltage density is white up to the avalanche frequency &ohgr;aand decreases inversely with current. For &ohgr; ≫ &ohgr;athe spectral noise power density falls off with &ohgr;4.