This paper presents an analysis of lifetime versus excess density or photoconductivity versus excitation intensity for a semiconductor when two or more trapping levels are present. As an example, data for ap‐type (boron‐doped vacuum‐float‐zone grown) silicon sample which had been irradiated with Co60&ggr; rays are considered. Measurements covered seven orders of magnitude in photoconductivity, and the lowest excess electron concentration was ∼ 10−8times the equilibrium hole concentration. Two trap levels were identified atEc−(0.56±0.01) eV andEc−(0.71±0.02) eV. Introduction rates for these levels were ∼ 10−6and ∼ 10−8(photon cm)−1, respectively.