It has been confirmed that avalanche multiplication occurs in amorphous semiconductors, especially in amorphous selenium. The obtained hole and electron ionization rates, β and α, have single exponential dependence on the reciprocal electric field. This phenomenon has been successfully applied for the first time to a highly-sensitive image-pickup tube with quantum efficiency as high as 10. This avalanche vidicon has excellent S/N characteristics. This may be due to the large ratio of hole to electron ionization rates from the shot noise analysis.