High voltage three-phase cable comprising three cores positioned so as to assume the configuration with minimum radial dimension and a sheath surrounding the three cores, wherein each core comprises an electric conductor having a substantially triangular shaped cross section with vertex portions and edges; an insulating system surrounding the electric conductor, the insulating system comprising an inner semiconducting layer surrounding the electric conductor, an insulating layer surrounding and in contact with the inner semiconducting layer and an outer semiconducting layer surrounding and in contact with the insulating layer, the layers of the insulating system being made of an extruded polymeric material having a dielectric constant ε comprised from 2 to 2.5; and a metallic screen surrounding the insulating system.