AbstractThe carrier transport in inhomogeneous solids is reevaluated in respect to the differences between a built‐in field within a space charge region and an external field, and related to differences in carrier redistribution and carrier heating, resulting in a different field‐dependence of the mobility. With the assistance of electrostatic and electrochemical potential distributions the regions of substantial carrier heating can be identified as regions in which the current is carried by diffusion only (DO), or by drift only (DRO) in forward (or low reverse), and in high reverse bias respectively, and are distinguished from the region of a major electrostatic potential drop (Boltzmann region) in which the net current is small compared to drift and diffusion. In junction devices major carrier heating does only occur in DO‐ and DRO regions, and only for minority car