In a Rochow process, organohalosilanes are prepared by reacting metallic silicon particles with an organohalide in the presence of a copper catalyst and a co-catalyst. The invention uses as the co-catalyst a powder of co-catalyst active element-copper alloy containing substantial strain energy because this co-catalyst can reduce the activation time taken until a steady state is reached, which has been an outstanding problem in Rochow reaction, maintain the steady state over time and increase the selectivity of desired diorganodihalosilane for eventually increasing the yield based on the starting silicon.