Results from MOCVD grown n-Al0.1Ga0.9N/i-GaN/p-GaN UV photodetectors on sapphire substrates are presented. The devices show peak responsivities near 0.2A/W for wavelengths between 352nm and 362nm, and responsivities of less than 10-3A/W for wavelengths longer than 375nm and shorter than 342nm. The data is explained in terms of a simple device model.