We report here the successful fabrication of a planar, low dark current, and high sensitivity In0.4Ga0.6Asp‐i‐nphotodiode fabricated on a semi‐insulating GaAs substrate with the aid of a multistage strain‐relief buffer system. Without using surface passivation and anti‐reflection coatings, the detector has a quantum efficiency of 42% and a peak responsivity of 0.45 A/W at 1.3 &mgr;m wavelength. The reverse leakage current for the mesa‐etched photodiode with an active area of 2×10−4cm2is 5×10−9A at −5 V, and the breakdown voltage exceeds 25 V.