Abstract: A process and apparatus for producing polycrystalline silicon ingots. A crucible is arranged in a process chamber and filled with solid silicon material. At least one diagonal heater is located laterally offset to and generally above the silicon ingot to be produced. The silicon material is heated to form molten silicon in the crucible, and thereafter cooled down below the solidification temperature of the molten silicon. A temperature profile in the silicon material during the cooling phase is controlled at least partially via the at least one diagonal heater. The apparatus includes a process chamber, a crucible holder, and at least one diagonal heater. The diagonal heater is located laterally with respect to the crucible holder and generally above a polycrystalline silicon ingot to be formed in the crucible. The diagonal heater is stationary with respect to the crucible holder when the process chamber is closed.