A transient model of a stagnation point flow, single wafer reactor is used to predict the concentrations of tungsten hexafluoride and dichlorosilane as a function of position along the surface of a six inch wafer during the transient and steady state operating phases of tungsten silicide deposition in trenches having an initial aspect ratio of five. We analyze two startup protocols: 1. The susceptor temperature setpoint is changed from just above room temperature to its steady state value after the reactant flows are established. 2. The reactant flowmeter setpoints are changed to their steady state values after the wafer temperature is established in a flow of inert gas. A ballistic transport and reaction model is used to predict film thickness and composition profiles of these tungsten silicide films as a function of deposition time. The transient portions of the two startup protocols do not affect film profiles or average composition as much as the inherent increase in aspect ratio as the fill proceeds.