Custom-made Ge and InGaAs photodiodes were tested for high sensitivity dc and ac radiometric applications. Equal size, large-area photodiodes were selected and used as optical sensors in NIST's near-infrared (NIR) standard radiometers. The dc electronic characteristics of the Ge and InGaAs radiometers were measured versus photodiode temperature. At minus 30 degrees Celsius, a limit-sensitivity of 22 fA and a dark-current stability of 0.2 pA/16 hours was achieved with the InGaAs radiometer, which was three times better than the results obtained with the Ge radiometer. The Ge radiometer was used for dc signal measurements only, because at frequencies higher than 0.3 Hz the noise boosting effect decreased the photocurrent sensitivity. The frequency dependent gain characteristics were calculated and compared for the two types of radiometer. The InGaAs radiometer could measure optical radiation with a chopping frequency of 10 Hz without any response or limit-sensitivity degradation.