High pressure spatial chemical vapor deposition apparatuses and related process are disclosed for forming thin films on a substrate. An enclosure includes plural process chambers fluidly isolated from each other by radial separating barriers. Each chamber contains a different source gas comprising one or more volatile reactive species. The substrate is supported beneath the chambers on a rotating heated susceptor. Rotation of the susceptor carries the substrate in a path which consecutively exposes the substrate to the volatile reactive species in each process chamber. The gases first mix in the gaseous boundary layer formed adjacent the substrate. A thin film gradually grows in thickness on the substrate with each successive pass and exposure to the volatile reactive species in each of the individual process chambers. The film may be grown at high pressures exceeding 1 atmosphere in some implementations. A modular design includes an outer shell and different interchangeable process inserts.