To understand the relationship between the work function and structural properties of sufficiently expanded triangular defects (size: ∼250 μm) in the 4H-SiC epitaxial layer, Kelvin probe force microscopy (KPFM) and spectroscopic [micro-Raman spectroscopy and photoluminescence (PL)] analyses were performed. Spectroscopic analysis demonstrated that the triangular defects mostly comprise the 3C polytypes and that it experiences internal stress, defects, and defect-induced carrier generation. The distinguishable areas in the triangular defects had surface potential values different from those of the 4H-SiC matrix; this could be explained by the work function difference, which arises from variations in the electron affinity of the 3C polytype as well as the positional variations of the Fermi energy level in terms of electron concentration. In addition, tensile-stress-induced surface disorder leading to variations in electron affinity was discussed. The mechanical properties of the triangular defects measured by a nanoindenter were significantly deteriorated because of many dislocation arrays and stacking faults with many broken and/or strained bonds.