Front illuminated In0.53Ga0.47As photodiodes with different mesa structures were fabricated on the materials of PIN InP/ In0.53Ga0.47As /InP by wet etching.The characteristics of these diodes,such as dark current,signal and noise were compared,and the influence of mesa structures was analyzed.The results indicated that the dark current and noise of diodes are linear with mesa area,but the signal is not.Mesa of diode consists of the sensitivity area and the outside section of the sensitivity area.The outside section of the sensitivity area does contributions to the dark current and noise in the same way as sensitivity area,but the outside section′s contribution to the signal is not in accord with the one of the sensitivity area.That is mainly because of the reflection of substrate and the transverse diffusion of carriers generated by the absorption in the spacing between pixels.