We propose and demonstrate an all‐epitaxial semiconductor/semimetal Schottky (S3) photodiode based on ann‐type Hg0.56Cd0.46Te/HgTe isotype heterojunction. The structure, grown using molecular beam epitaxy, was fabricated into back‐illuminated mesa diodes. A 40‐&mgr;m‐diam photodiode shows room‐temperature rectification and high efficiency photoresponse, with a long‐wavelength cutoff of 2.43 &mgr;m and a peak quantum efficiency of 44% at 2.0 &mgr;m for 250 mV of reverse bias. The dark current at this bias is 100 &mgr;A.