Specially designed experiments were performed for the validation of direct simulation Monte Carlo calculations of rarefied internal gas flows. Hot zinc vapor was released into a cold-wall deposition chamber filled with a background gas at low pressure in which two silicon wafers were mounted. The deposited zinc layers on these wafers have been measured in four different experiments, with varying background gas species (argon and helium) and background pressures (0.031-0.25 Pa). The background gas conditions were chosen such that the Knudsen numbers based on the zinc mean free path range from 0.34 to 2.8. The experimental results have been compared to simulation results. (C) 2007 American Vacuum Society.