A method for making a large surface area silicon filament for production of bulk polysilicon by chemical vapor deposition (CVD) includes melting silicon and growing the filament from the melted silicon by an EFG method using a shaping die. The cross sectional shape of the silicon filament is constant over its axial length to within a tolerance of 10%. In embodiments, a plurality of identical and/or dissimilar filaments are grown simultaneously using a plurality of shaping dies. The filaments can be tubular. Filament cross sections can be annular and/or can include outwardly extending fins, with wall and/or fin thicknesses constant to within 10%. Filaments can be doped with at least one element from groups 3 and 5 of the Periodic Table. The filament can have a length equal to a length of a specified slim rod filament, and a total impedance not greater than the slim rod impedance.