The hydrodynamic and convection heat transfer performance of Polydimethylsiloxane (PDMS) microchannels with three different micropillar array assemblies ranging from a porosity of 0.8 to 0.91 are investigated and compared under single-phase and two-phase conditions. Dielectric coolant FC-3283 is employed and permeability measurements are made for flow rates ranging from 53 kg/m²s to 369 kg/m²s. An analytical model is developed to quantify the deformation of PDMS microchannels with micropillar arrays under forced flow conditions. The heat transfer performance is experimentally evaluated using the same fluid for flow rates ranging from 105 kg/m²s to 420 kg/m²s with heat fluxes ranging from 1.5 W/cm² to 16 W/cm². High-Speed Imaging is performed to study the two-phase flow characteristics.