Carrier gas flow in a rapid thermal chemical vapor deposition (RTCVD) reactor was studied using flow visualization and laser induced Rayleigh light scattering (RLS). The flow field consists of a downward axisymmetric jet of carrier gas impinging on a wafer which undergoes transient heating. Flow visualization results showed three stable flow regimes as the surface rose from ambient to high temperature: momentum dominated, buoyancy dominated, and a second momentum dominated regime at high temperature; each separated by unstable, chaotic flows. RLS temperature measurements provided transient gas temperature histories, documenting flow visualization results. Regions of momentum dominated, buoyancy dominated, and unstable flows were defined as a function of Grashof number, Reynolds number, pressure, and wafer temperature.