Ce 4f derived states at the Fermi level (EF) of the isostructural single crystals CeRhAs, CeRhSb, and CePtSn were observed directly by means of high-resolution (ΔE = 18-20 meV), low-temperature (10-12 K) photoemission spectroscopy with a photon energy of hv = 126 eV. The Ce 4f spectrum for the Kondo semiconductor CeRhAs exhibited no peak structure near EF, and its spectral intensity decreases monotonically above the binding energy ∼90 meV, thereby forming a large gap structure. The spectrum of the semimetal CeRhSb is enhanced above ∼120 meV, but decreases steeply above ∼13 meV, which indicates the existence of a narrow pseudogap at EF. A clear crystal field excitation at ∼27 meV, and a weak Kondo resonance at EF, were found in the metal CePtSn.