Silicide based oxidation resistant coatings were developed over Mo-30 W wt.% alloy using halide activated pack cementation process. Formation of single-layer [only (Mo,W)Si2] and double-layer [consisting of (Mo,W)Si2 outer and (Mo,W)5Si3 intermediate] coatings were developed below and above a critical coating temperature of 1100 °C using a pack mixture having a composition of 20Si-2.5NH4F-77.5Al2O3 (wt.%). The activation energy for the growth of (Mo,W)Si2 coating layer was found to be 51 kJ/mole. The diffusion mechanism of the species in (Mo,W)-(Mo,W)Si2 system (using single layer coated samples) was studied by conducting isothermal annealing experiments at different temperatures of 700, 800 and 1000 oC for a period of 1000 h. The growth rate of the (Mo,W)5Si3 interlayer during the isothermal annealing treatment was found to be parabolic. The mechanism of the formation of (Mo,W)5Si3 intermediate layer, its microstructure and growth kinetics in (Mo,W)-(Mo,W)Si2 system were investigated by cross-sectional electron microscopy and EBSD analysis. The growth mechanism of the intermediate layer was further discussed using a Physico-chemical approach.