A lateral structure metal‐semiconductor‐metal photodiode has been fabricated on GaInAs, in which an AlInAs/GaInAs graded superlattice has been incorporated. This photodiode has exhibited a dark current lower than 100 nA, an internal quantum efficiency of greater than 80% at a wavelength of 1.3 &mgr;m, and a capacitance of 40 fF, all at the bias voltage of 10 V. The response speed of this photodiode has been characterized by electro‐optic sampling to exhibit a full width at half maximum of 14.7 ps.