We report the firstp‐njunction delineation and diffusion study in a ternary chalcopyrite‐type semiconductor.p‐njunctions were formed in Zn‐ or Cd‐platedp‐CuInSe2by 5‐min anneals at 200–450 °C. By means of angle lapping and staining techniques, junction depthsxjvarying from ∼1 &mgr;m to ∼130 &mgr;m were determined. These measurements yield the relationship lnxj(&mgr;m) =14.31−6900/T(K). The interdiffusion coefficient derived fromxjisD(cm2/sec) =164 exp[−1.19 (eV)/kT]. The large preexponential term indicates concentrations or mobilities of point defects substantially above those of the related II‐VI compounds.