Abstract
A novel physical mechanism is proposed as an explanation of intrinsic self-generated chaotic oscillations in semiconductors under static external conditions. It is based upon impact ionization from at least two impurity levels, and includes trapping and dielectric relaxation. Conditions for an oscillatory instability are derived, singling out high-purity relaxation semiconductors with low differential mobility. A period-doubling route to chaos and a strange attractor of spiral type are found.