The present invention relates to a semiconductive polymer composition comprising an olefin homo- or copolymer wherein the composition has a direct current volume resistivity of less than 1000 Ohm·cm at 90° C., an elongation at break which after aging for 240 hours at 135° C. does not change by more than 25%, and a total number of structures of 20 or less in the SIED test. Furthermore, the present invention relates to an electric power cable comprising a conductor, a semiconducting layer and, adjacent to the semiconducting layer, an insulation layer, wherein the semiconducting layer is formed by said semiconductive polymer composition and to the use of said semiconducting polymer composition for the production of a semiconductive layer of an electric power cable.