Abstract The chemical erosion of carbon was investigated in the linear plasma device Pilot-PSI for ITER divertor relevant hydrogen plasma flux densities 1023<Γ<1025m−2s−1. The erosion was analyzed in situ by optical emission spectroscopy and post mortem by surface profilometry. The experiments indicate a threshold for the absolute carbon erosion rate as a function of plasma temperature Te around 0.7eV, a peak of the surface temperature around 550°C, and no dependence on plasma flux density. The latter implies a flux dependence of the chemical erosion yield as Γ−1. The value of the chemical erosion yield at the surface temperature of maximum erosion and Γ=1×1024m−2s−1 was 0.9% for Te<0.5eV as determined by surface profilometry.