Successful growth of lattice‐matched Sc1−xErxAs layers buried in GaAs with a room‐temperature resistivity of ∼50 &mgr;&OHgr; cm demonstrates the feasibility of fabricating heterostructures of lattice‐matched rare‐earth monopnictides and monochalcogenides in semiconductors. Reflection high‐energy electron diffraction oscillations during ScAs, ErAs, and Sc1−xErxAs growth indicate monolayer‐by‐monolayer growth.