Carbon dioxide (CO2) is increasingly being used as a highly efficient, environmentally friendly and sustainable refrigerant/heat transfer fluid. Because of its high specific heat and cooling capacity, supercritical CO2 has the potential to be widely used in a range of applications, such as power generation and thermal management of data centers/electronics. Near the critical condition, the thermo-physical properties undergo drastic changes, which includes a boiling-like phenomenon in the supercritical region (pseudo-boiling), which can affect the heat transfer performance. Thus, knowledge about the heat transfer process in the supercritical phase of CO2 is necessary. In this experimental study, the heat transfer characteristics of supercritical CO2 near the critical condition, along with pseudo-boiling, in a parallel-flow microchannel and a micro-jets impingement device were studied. An experimental setup, microfluidic devices with embedded resistance temperature detectors (RTDs), and a LabVIEW data acquisition system (DAQ), were used to obtain data for a range of variables, such as temperature, pressure, heat flux, and mass flux. Heat transfer coefficients (HTC) were calculated for different flow conditions (i.e., mass fluxes and pressures). In addition, the effect of the downstream position was discussed. Also, in addition, while studying the pseudo-boiling effect, heat transfer coefficients were calculated both during the pseudo-boiling condition and before and after pseudo-boiling. A pseudo-boiling mass quality, xpb, is proposed that provides an account, pertinent to the heat transfer coefficient, of the transition across the region affected by the Widom line, assuming values between 0 and 1, corresponding to the borders of the pseudo-boiling regions. The development of xpb required quantifying the specific enthalpy change through the pseudocritical region, systematically obtained using a pertinent equation of state. A dimensionless pseudo-boiling heat transfer coefficient enhancement coefficient, E=hpb/hl, was then proposed and examined as a function of the mass quality. (hpb is the heat transfer coefficient in the pseudo boiling region and hl is the heat transfer coefficient of the single-phase liquid-like region.) The usefulness of the pseudocritical mass quality to reveal the effect of the transition across the Widom line was then demonstrated based on experimental results obtained with CO2. The results were then compared for parallel-flow microchannel and micro-jets impingement device, and discussed accordingly. The independent variables included mass fluxes ranging from 1825 kg/m2.s to 8080 kg/m2.s, reduced pressure (p/pR) ranging from 1.02 to 1.143, and heat fluxes up to 98 W/cm2.