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This paper discusses the limitations of germanium-junction transistors at elevated operating temperatures. The limiting factors are a consequence of increased thermal hole-electron pair generation at higher temperatures. This causes an increase in collector "leakage" current, which affects the base current. Thus, due to the base-lead resistance, the emitter to base-bias conditions are changed. The problems associated with power transistors are discussed, including cooling of the unit, current and voltage limitations, and reduction in base-lead resistance. It is pointed out that, in addition to bias changes, base lead resistance also causes a power loss which becomes important at the high currents used in power units. Examples of liquid convection cooled and metallic conduction cooled n-p-n and p-n-p power transistors are described. Satisfactory "alpha" values are maintained to collector currents of over one hundred milliamperes. In class A operation power gains exceeding 30 db and efficiencies close to the theoretical limit of 50 per cent are obtained at 1 watt dissipation levels.