Spatially resolved SiH3 measurements are performed by cavity ring down spectroscopy on the SiH3 (A) over tilde (2)A(1)<--(A) over tilde (2)A(1) transition at 217 nm in a remote Ar-H-2-SiH4 plasma used for high rate deposition of hydrogenated amorphous silicon. The obtained densities of SiH3 and its axial and radial distribution in the cylindrical deposition reactor are compared with simulations by a two-dimensional axisymmetric fluid dynamics model. The model, in which only three basic chemical reactions are taken into account, shows fairly good agreement with the experimental results and the plasma and surface processes as well as transport phenomena in the plasma are discussed. Furthermore, the SiH3 density determined by cavity ring down spectroscopy is in good agreement with the SiH3 density as obtained by threshold ionization mass spectrometry.