This book demonstrates the role and abilities of fluctuation in semiconductor physics, and shows what kinds of physical information are involved in the noise characteristics of semiconductor materials and devices, how this information may be decoded and which advantages are inherent to the noise methods. The text provides a comprehensive account of current results, addressing problems which have not previously been covered in Western literature, including the excess noise of tunnel-recombination currents and photocurrents in diodes, fluctuation phenomena in a real photoconductor with different recombination centers, and methods of noise spectroscopy of levels in a wide range of materials and devices.