Abstract The photoelectrochemical oxidation of n-type 4H–SiC in KOH solution shows surprising features. While a limiting anodic photocurrent is observed at low light intensity, the semiconductor passivates at high intensity. The photocurrent corresponding to the passivation peak increases linearly with photon flux but decreases when mass transport in the system is enhanced. Characteristic current oscillations are observed. Possible reasons for these results are considered, as is the use of photoanodic etching for practical applications.