Xenon flash lamp with 100 s pulse duration was used to enhance the performance of large area (1 cm2) diffused silicon photodiodes. Leakage current, rectification, and photoresponse of silicon photodiodes after flash lamp annealing (FLA) as function of the number of shots were investigated. The experimental results show a significant improvement in photodetector properties after annealing and the best annealing condition obtained with 11 shots. No shift in peak response of photodetector is observed after FLA. Furthermore, the stability of photodiode was investigated.