The thermoelectric effect is important for thermal sensing, energy harvesting and other applications. This paper investigates the Seebeck coefficient of silicon carbide (SiC) on silicon (Si) heterojunctions and discusses the mechanism underlying the observed effects. The measured Seebeck coefficients of p‐3C‐SiC/p‐Si and n‐3C‐SiC/p‐Si heterojunctions are much higher than other reported values for SiC materials. The maximum Seebeck coefficients of p‐3C‐SiC/p‐Si and n‐3C‐SiC/p‐Si obtained were 1720 µV/K at 383 K and –421 µV/K at 396 K, respectively. These values are almost three times higher than those of other p-SiC and n-SiC materials. The high Seebeck coefficient in SiC/Si heterojunctions is attributed to the unique structure of the heterojunctions, which enables thermally activated charge carriers to migrate from Si to SiC. The results suggest that these heterojunctions can be exploited to develop highly sensitive self-powered thermal sensors.