The current leakages of InAs photodiodes have been systematically studied by adding undoped layers having thicknesses of 0, 0.30, and 0.72 mum between the p-n junction. At reverse bias V = - 0.5 V, the dark currents of the InAs p-i-n diodes with undoped layer thicknesses of 0, 0.30, and 0.72 mum are about 5 x 10(-6), 7 x 10(-8), and 1 x 10(-10) A, respectively, at 77 K. The leakage current of the InAs p-n diode was successfully reduced by adding 0.72-mum-thick undoped layer between the p-n junction.