A growing concern in the electronics industry is the need to remove large amounts of heat from small areas with high chip density. Carbon nanotubes possess very high intrinsic thermal conductivity (~3000 W/mK) and have received considerable attention for their ability to enhance thermal interface conductance. Here, we consider in detail the effects of the catalyst structure used to create MWCNT arrays by microwave plasma-enhanced CVD and its influence on the diameter, quality and thermal interface resistance. Using modified, nearly monodispersity Fe₂O₃ nanoparticles derived on an amine-terminated fourth-generation poly(amidoamine) (PAMAM) dendrimer, vertically oriented MWCNT arrays of variable diameter distributions and quality were grown with high reproducibility. The amount of Fe(III) used for complexation with the dendrimer ‘nanotemplate' and the calcination temperature of the dendrimer-templated Fe nanocomposites formed are the parameters that have been employed to modify the catalyst structure. The effect of the calcination temperature of the catalysts on the diameter distribution of MWCNTs diminishes as the amount of Fe(III) decreases. The calcination of catalysts with dendrimer:Fe molar ratio of 1:46 at 250, 550, 700 and 900 °C resulted in the growth of MWCNTs with corresponding diameter distributions of 20–40, 25–50, 50–90, and 40–60 nm, respectively. The quality of MWCNTs, for the most part, increased with decreasing catalyst amount. They were few nanotubes (<10%) with diameters either less or greater than the range given above; the smaller-diameter nanotubes were mainly as a result of secondary growth. The diameter range of MWCNTs was obtained from a random statistical count of 140 nanotubes imaged by high resolution FESEM; resonance Raman spectroscopy was used to characterize the quality of the MWCNT arrays. The spatial density of MWCNTs for all the samples as determined by ImageJ was roughly the same, in the range of 65 to 70%. Mechanical tests carried out also revealed that the MWCNT arrays were well anchored on the Ti (30 nm)-coated SiO₂/Si substrate. Owing to its improved precision over traditional thermal interface resistance measurement techniques, the photoacoustic technique provides a reliable approach to characterize the thermal interface performance of the MWCNT arrays. The thermal interface resistance of the MWCNT arrays has shown close correlation with the quality or number of defect sites on the walls of the MWCNTs. The enhanced thermal interface performance of the MWCNTs suggest that real interfacial contact area may be increased by the additional conformability provided by MWCNT arrays with an increased number of defect sites and carbon impurities. This study contributes not only to the development of an active catalyst via a wet chemical based route for structure-controlled MWCNTs growth but also to the development of efficient and economic MWCNT-based structures that show low thermal interface resistance (£ 10 mm²K/W).