The alkylhalosilanes are directly synthesized by reacting an alkyl halide with silicon in the presence of a catalytically effective amount of (.alpha.) a copper metal or a copper-based compound catalyst and (.beta.) a catalyst promoter intermixture therefor which comprises an effective minor amount of an additive .beta.1 selected from the group consisting of tin, a tin-based compound and mixture thereof, an effective minor amount of an additive .beta.2 selected from the group consisting of cesium, potassium and rubidium, and compound and mixture thereof, and an effective minor amount of an additive .beta.3 selected from the group consisting of the element phosphorus, a phosphorus-based compound and mixture thereof.