There is a strong relation between the size, the shape and the location of the illuminated part of a shallow-junction photodiode, and its series resistance [2, 3, 4]. This relation creates an expectation for a big variation of the response time (the time for which the photo-generated charge will be removed from the photodiode) with the illuminated spot size. This is because the time constant of the photodiode, which is one of the main factors defining the response time, is a product of the series resistance multiplied by the junction capacitance. In this work the dependence of the charge removal time of a shallow photodiode on the size of the illuminated area, is studied. Simulation results, as well as measurement data, show that the response time is changing only slightly with the position and the size of the illuminated spot size, when very short light pulses are used. After the incidence light is over, the discharging of the photodiode continues with a time constant, which is highly independent of the size and the location of the illuminated part of the photodiode.