We grow a boron (B)-doped BaSi 2 (0.7 µm)/undoped n-BaSi 2 (1.7 µm) layered structure on a p-Si(111) substrate by molecular beam epitaxy, and observe the cross-sectional potential profile across the junction by Kelvin probe force microscopy (KFM). The potential increases when the KFM tip is moved from the B-doped BaSi 2 to the n-BaSi 2 , and decreases in the p-Si. Inflection points are clearly observed in the potential profile at the B-doped BaSi 2 /n-BaSi 2 and n-BaSi 2 /p-Si interfaces. Secondary ion mass spectrometry reveals that B atoms scarcely diffuse to the n-BaSi 2 layer. These results show the formation of a pn junction at the B-doped BaSi 2 /n-BaSi 2.