This paper investigated the hot deformation behavior of an AISI 4340 material through high-temperature compression experiments. The compression tests were performed to obtain stress-strain curves at processing temperatures of 900, 1,000, 1,100, and 1,200℃, and the strain rates of 0.01, 0.1, 1, and 10 s^-1 up to a true strain of 1.0 in the high-temperature compression mode of Gleeble^® 3,500. A novel 3D processing map, constructed through power dissipation efficiency and Ziegler"s instability criterion, is proposed. The deformation behavior was analyzed by observing changes in the microstructure from the high-temperature compression tests. Electron back scatters diffraction (EBSD) was used to characterize the microstructures for various processing parameters. The process workability of finite element analysis (FEA) was examined in the deformation flow instability map in the three-dimensional space for each strain. As a result, each particle"s strain rate and temperature of FEA data can be observed in a three-dimensional flow instability map to control the temperature and process speed to avoid unstable zones.