An optically reconfigurable gate array (ORGA), an alternative technology to commercially available field programmable gate arrays (FPGAs), is much faster. Moreover, it can operate in radiation-rich environments. An ORGA uses a laser array, a holographic memory, and an ORGA-VLSI chip including a fine-grained programmable gate array. Many configuration contexts can be stored on the holographic memory and can be addressed by the laser array. The ORGA-VLSI can be programmed optically through numerous photodiodes. To realize faster configuration, measuring the variation of photodiode characteristics is extremely important. Nevertheless, photodiode characteristics have not been estimated to date because measurements must be done using its programmable gate array such that the measurement results include a photodiode response time and propagation delay on the programmable gate array. They cannot be classified clearly. Therefore, this paper proposes a photodiode sensitivity measurement method using low light intensity. Results show that the measurement methodology can remove the propagation delay factor and can extract photodiode sensitivity.