My PhD study aims to address the current challenges in the experimental measurement of near-field thermal radiation and to further investigate its application for energy conversion. To this end, I propose to develop a versatile experimental setup for fundamental understanding and measurement of near-field thermal radiation that also includes the process of design and fabrication of proper samples. Using this setup, direct and systematic measurement of near-field thermal radiation between macroscale planar structures for broad nanoscale gap distances under a large thermal gradient over 100 K is achievable. . . Moreover, I will also study the feasibility of utilizing near-field thermal radiation to improve the conversion efficiency of current energy conversion schemes. In particular, I propose an alternative way of exploiting near-field thermal radiation for renewable energy harvesting that can be called near-field enhanced thermionic energy conversion (NETEC), to generate electricity directly from moderate to high temperature heat sources (i.e., 800 K<T<1600 K).