Chemical vapor deposition processes are one of the most used techniques for depositing thin films in the semiconductor-microelectronics and opto-electronic industries. Particulate contamination of the substrate during these CVD processes can be detrimental to the product yield. Due to the temperature gradients present in the CVD reactor, thermophoresis has a direct impact on the amount of particulate deposition on the substrate. The thermophoretic force is the force that arises from asymmetrical interactions of a particle with the surrounding gas molecules due to a temperature gradient. CVD processes can take place in hot and cold wall reactors, with varying substrate temperatures. This array of thermal boundary conditions results in a variety of temperature gradients and thermophoretic forces on the particle. There are other forces also acting on the particles in the CVD environment such as the Brownian force, drag, and gravity. The effect of thermophoresis on the particle transport and deposition in the reactor is examined. Different particle concentrations and sizes is considered in the reactor. The motion of these particles according to the thermal gradients in the reactor is examined. The behavior of these particles under different thermal conditions is studied.