The gold foil is split into two parts at the vertex of the plastic wedge, and forms two separate contacts with the p-type upper layer of the germanium substrate when the wedge is pressed against it by the spring. The two pieces of gold foil form the collector and emitter, and a metal electrode attached to the other side of the semiconductor forms the base electrode.
This file was derived from: Point-contact transistor.svg:
Point-contact transistor.svg: 忍者猫
derivative work: VectorVoyager