We have fabricated a metal‐semiconductor‐metal Schottky photodetector on a semi‐insulating InP substrate using a nominally lattice‐matched In0.52Al0.48As/In0.53(GaxAl1−x)0.47As (graded)/In0.53Ga0.47As structure grown by molecular beam epitaxy. On average the graded quaternary layer enhanced the responsivity by about 35% compared to an identical device without the graded region, reaching a maximum of 0.45 A/W at 10 V applied bias. The associated dark current was 95 nA; the dark capacitance was 90 fF. High‐speed measurements with a gain‐switched 1.3 &mgr;m laser diode demonstrated an instrumentation‐limited impulse response of 50 ps.