In the 1930s, the management of Bell Laboratories sought to develop a low-power, reliable, solid-state replacement for the vacuum tube used in telephone signal amplification and switching. Materials scientists had to invent methods to make highly pure germanium and silicon and to add controlled impurities with unprecedented precision. Theoretical and experimental physicists had to develop a fundamental understanding of the conduction properties of this new material and the physics of the interfaces and surfaces of different semiconductors. By investing in a large-scale assault on this problem, Bell announced the “invention” of the transistor in 1948, less than a decade after the discovery that a junction of positively and negatively doped silicon would allow electric current to flow in only one direction. Fundamental understanding was recognized to be essential, but the goal of producing an economically successful electronic-state switch was kept front-and-center. Despite this focused approach, fundamental science did not suffer: a Nobel Prize was awarded for the invention of the transistor. During this and the following effort, the foundations of much of semiconductor-device physics of the 20th century were laid.