Deep ultraviolet Al0.75Ga0.25N metal-semiconductor-metal photodetectors with high Al concentration have been demonstrated. A metal-organic chemical vapor deposition grown high quality Al0.75Ga0.25N layer was used as a template. Spectral responsivity, current-voltage, optical transmission, and noise measurements were carried out. The photodetectors exhibited a 229 nm cutoff wavelength and a peak responsivity of 0.53 A/W at 222 nm. Some 100x100 mu m(2) devices have shown a dark current density of 5.79x10(-10) A/cm(2) under 50 V bias. An ultraviolet-visible rejection ratio of seven orders of magnitude was obtained from the fabricated devices.