Siliconization and the simultaneous siliconization and nitridation (siliconitridation) of AISI316 stainless steels were studied by chemical vapor deposition in a fluidized bed reactor. Several beds of particles were used: a single bed of silicon particles, a double bed of silicon and alumina particles and a single bed of alumina particles. In most of the experiments, the precursors for the deposition process were generated in situ by reaction of HCl with Si particles of the bed. After siliconization at 500 °C during 30 min a Si surface concentration of 30 at.% was achieved. The siliconitridation experiments yielded two different surface compositions: a mixture of iron silicide and chromium nitride and, under other conditions, a silicon nitride thin film. These results are in agreement with thermochemical calculations presented in the paper.