Nitride-based AlGaN/GaN heterostructure two-dimensional electron gas photodetectors have been successfully fabricated by low-pressure metalorganic vapor phase epitaxy on sapphire substrate. By using such an AlGaN/GaN heterostructure, we could significantly reduce the recombination of photogenerated carriers and thus achieve extremely high photodetector responsivity due to the use of AlGaN/GaN heterostructure. With an incident light wavelength of 270 nm, it was found that the AC responsivity could reach 8.7 x 10(6) A/W. (C) 2003 Elsevier Ltd. All rights reserved.