At the present time, silicon and InGaAs/InP photodetectors from different manufactures have rather low level of noise, a good uniformity of the surface response as well as a wide dynamic range and linearity. For these reasons they are exploited in the instruments for measuring optical radiation within the near infrared range 800-1600 nm. Furthermore, the silicon and InGaAs/InP photodetectors are used for maintaining the scales of spectral responsitivity in the above-listed spectral range in many laboratories. Due to the last application, we presented our studies of the reflectance and the internal quantum efficiency inherent in silicon and InGaAs/InP photodiodes from different manufactures. Both the reflectance and the internal quantum efficiency determine the photodiode spectral responsivity, which is the radiometric characteristic of interest in the fields where these devices can be used for optical radiation measurements. The responsivity will be known if both the reflectance and the internal quantum efficiency are known at every wavelength We have measured the reflectance of three silicon photodiodes and three InGaAs/InP photodiodes that were practically used to maintain scale of the spectral responsivity in the Institute for Applied Physics (CSIC). The results obtained show that we have an outstanding change between the reflectance of the photodiodes of the same set, which indicates that its necessary to measure the reflectance of every individual photodiode if an accurate reflectance knowledge is needed, its necessary to measure the reflectance of every individual photodiode to have a precise knowledge on the evolution of its reflectance.