We report on deep ion-implantation of sulfur into InP substrates to replace the epitaxial subcollector layer of double-heterojunction bipolar transistors. Using optimized implantation conditions of 350 keV energy and 1× 1015 cm-2 dose, we achieved a subcollector sheet resistance of 15 Ωsquare. Under well-controlled regrowth conditions a root-mean-square roughness of 12 Å is measured from DHBT epitaxial layers grown on implanted InP substrates, comparable to DHBT epitaxial layers grown on n+ epiready unimplanted substrates. We observe a pronounced increase in surface roughness of epitaxial layer beyond a threshold ion dose, depending on implantation energy. Large-area DHBT devices result with sulfur-ion implanted subcollector shows similar characteristics compared to devices fabricated on n+ -doped InP substrates.