Single crystals of were pulled without rotation from the melt in the presence of tellurium or selenium impurity employing a Czochralski‐type apparatus. The formation of pronounced periodic and nonperiodic impurity striations was observed; their appearance and origin were studied as a function of the thermal conditions prevailing in the immediate vicinity of the solid‐melt interface. It was concluded that the formation of such striations is the result of temperature fluctuations at the interface brought about by convection currents in the melt which in turn are caused primarily by sharp temperature gradients in the growing crystal near the interface.