The Sm2O3/n-Si heterojunction has been fabricated by deposition of Sm2O3 thin film on n-type (100) silicon substrate using radio frequency (RF) magnetron sputtering followed by postannealing treatment. The obtained Sm2O3 thin film exhibited C-type cubic crystal structure with bandgap of ~4.1 eV. The Sm2O3/n-Si heterojunction showed an obvious rectification characteristic with turn-on voltage of 0.5 V and a decrease of resistance with increase of temperature, indicating typical semiconductor behavior. The heterojunction showed fine and stable ultraviolet photoresponse to illumination by 254-nm light. This combination of a wide-bandgap semiconductor with silicon might enable future applications in ultraviolet photodetection.