Hyperbranched poly(ether ketone)s (PEK's) were synthesized via A(3) + B-2 polymerization approach without forming cross-linked products, because the polymer-forming process based on Friedel-Crafts reaction was kinetically controlled by the solubility difference of monomers in the viscous hydrophilic reaction medium, poly(phosphoric acid) (PPA)/phosphorus pentoxide (P2O5). The hydrophilic trimesic acid as an A(3) monomer is soluble in the reaction medium, while hydrophobic diphenyl ether and 1,4-diphenoxybenzene as B-2 monomers are marginally soluble. It is hypothesized that the gelation was avoided because of the following two factors: (i) self-regulated feeding of the arylether monomers into the system driven by their poor solubility and phase separation from PPA/P2O5 medium; (ii) reaction-medium-induced isolation of growing macromolecules promoted by the high bulk viscosity. Both polymerization experiments based on equimolar or equifunctional stoichiometry (A(3):B-2) resulted in completely soluble hyperbranched PEK's in polar aprotic solvents when these polymers contained a little amount of solvent residues and only in strong acids if they were rigorously dried. The structural analysis by using MALDI-TOF mass spectroscopy in the low molar mass region provided further confirmation that there was no trace of networks; various sizes of cyclics were detected instead.