Iron‐doped epitaxial layers were grown using the vapor phase system and with a new doping method. The characteristics of the iron‐doped layer were investigated, and the layer was used as the buffer layer of the epitaxial layer for FET. It was found that the iron concentration in the epitaxial layer was proportional to the vapor pressure of the iron‐doping gas . The layer with a resistivity higher than 104 Ω‐cm could be prepared without increasing the crystal defects and impurities except iron. It was observed that the electrical characteristics of the submicron active layer on the chromium‐doped substrate were improved by the insertion of the iron‐doped buffer layer between the active layer and the substrate. It was found that the performance of FET's fabricated of the epitaxial layer was the iron‐doped buffer layer was higher than the performance of those without the buffer layer.