Transistor action at temperatures from 20 to 450 °C has been demonstrated forp+n−pp+bipolar structures fabricated in GaP. Improvements in the materials technology were essential to successful fabrication of these devices. The structural configuration chosen could also be used as a junction field‐effect transistor although this mode of operation was limited by the initial design to lower operating temperatures. While present device characteristics are restricted by ohmic contact resistance, this does not appear to be a fundamental limitation. These results demonstrate that GaP is a good materials candidate in which to base a technology for active electronic components operated at high temperatures.