Coulomb-blockade transport via donors working as quantum dots (QDs) in Si nano-transistor channels opens new pathways for atomic-level applications, but position-control of such QDs remains challenging. Here, we demonstrate that multiple-donor cluster-QDs can be formed by CMOS-compatible selective-doping, as observed from Coulomb-blockade transport at low temperature (T = 5.5 K). While at high gate voltage electron tunneling takes place via extended QDs, likely due to line edge roughness of the nanoscale channel, at low gate voltage tunneling occurs via a cluster of intentionally-doped donors. For the interpretation, we introduce a model of an isolated donor-cluster as a QD with voltage-dependent tunnel resistances. © 2019 The Japan Society of Applied Physics.