A variety of silicon carbide (SiC) detectors have been developed to study their sensitivity, including Schottky photodiodes, p-i-n photodiodes, avalanche photodiodes (APDs), and single photon-counting APDs. Due to the very wide bandgap and thus extremely low leakage current, SiC photo-detectors show excellent sensitivity. The specific detectivity, D*, of SiC photodiodes are many orders of magnitude higher than the D* of other solid state detectors, and for the first time, comparable to that of photomultiplier tubes (PMTs). SiC APDs have also been fabricated to pursue the ultimate sensitivity. By operating the SiC APDs at a linear mode gain over 106, single photoncounting avalanche photodiodes (SPADs) in UV have been demonstrated.