This paper presents first results of 200 mm diameter semi-insulating (SI) GaAs crystal growth experiments. The LEC method was used on condition that temperature gradients in critical regions can be controlled adequately. For furnace design and process parameter evaluation, powerful numerical simulation was indispensable. The structural and electrical properties of crystals grown by this temperature gradient controlled LEC method are similar to those known for state-of-the-art 150 mm SI GaAs crystals.