A study of thermal characteristics for uncooled CPV in addition to fluid flow and thermal characteristics for CPV integrated with a three dimensional (3D) rectangular shaped microchannel heat sink (MCHS) is numerically investigated. Steady and laminar flow of water as a coolant is used in the present study. The model is validated using different sets of data in the literature. For the cooled CPV system, the flow and thermal fields are analyzed using various channel number (N=26, 52, 78 and 104), concentration ratio (CR) ranged from 1 to 20 and mass flowrate ranged from 200 to 2000 g/min. For the uncooled CPV system, the CR ranged from 1 to 2.5. The parameters such as solar cell temperature, temperature uniformity, electrical efficiency, electrical power, net gained power, thermal power and thermal efficiency are evaluated from the simulation. Based on the obtained results, for the uncooled system, the CR of 2.5 is the maximum value that can be used where the solar cell temperature reached to the maximum allowable temperature of 85.48 ℃. For the cooled system, the results show that at CR of 20 and mass flowrate of 200 g/min, increasing the channel number from 26 to 104, significantly decrease the solar cell temperature from 93.2 ℃ to 87.3 ℃. As the concentration ratio increases, the cell efficiency decreases due to the increase in the cell temperature while the electrical power increases. Increasing the mass flowrate provides a remarkable enhancement in the thermal efficiency. For instance, at CR equals 20 and N of 26, increasing the mass flow rate from 200 g/min to 2000 g/min increases the thermal efficiency from 43% to 71.7%.