Semiconductor devices are very sensitive to surface contamination, and soldering flux is like a death warrant to the device. It is possible to do most of the soldering on these devices without flux by using the correct materials, temperature, and atmosphere. Illustrations of examples of how this has been done are shown. Some of the requirements for various applications are given. Certain metals, if used on semiconductor materials, may give trouble even if they occur only as an impurity in the solder. These metals are noted along with the effects they would have.