The effects of high temperature on an asymmetrically doped vertical pillar-type metal-oxide-semiconductor field-effect transistor (MOSFET) were investigated. An asymmetrically doped source and drain (SD) can be easily formed in a vertical pillar-type FET due to the unique pillar structure. When high temperature is applied to the asymmetric SD of a vertical pillar-typed silicon nanowire, it affects mobility and carrier injection differently. It decreases mobility by phonon scattering for heavily doped S and intermediately doped D. In contrast, it enhances carrier injection for intermediately doped S and heavily doped D. Thus the ON-state current (I-ON) shows opposite dependencies at high temperature. This tendency was verified by electrical measurements and supporting simulations.