A molecular‐beam source utilizing single‐filament construction to generate a reproducible and uniform beam of elemental molecules is presented. The filament design is constructed to conform to the shape of pyrolytic boron nitride crucibles utilized in molecular‐beam epitaxy (MBE) systems, and to minimize the thermal gradient between the crucible opening and the crucible bottom which is inherent in Knudsen cell technology. The design also improves heat transfer, efficiency, and flux response of the cell. We show that this cell exhibits a better flux response than typical commercially available effusion cells and successfully prevents source material redistribution, thus providing for long‐term flux stability and reproducibility in certain materials used in MBE. No increase in background impurity concentration in epitaxial AlGaAs films was observed, when compared to films grown using a standard Varian effusion cell. This cell is currently installed and being used as an aluminum source in a Varian GEN II system.