Transistorized computer logic has made steady progress toward higher speeds by reducing the dimensions of circuits and devices. However, even though circuit and device speeds have increased by three orders of magnitude, voltage, current, and power levels have remained about the same. Power dissipation at increasingly higher current densities seems to be leading to difficult thermal problems that will eventually limit the progress of logical circuitry toward higher speeds. This article examines these physical problems and limits, and offers the most directly effective solution to the dilemma—lower operating temperature. © 1969 IEEE. All rights reserved.