An experimental study of a microwave reflection arrangement used to measure changes in the conductivity of semiconductor samples is presented. A germanium sample with associated microwave circuitry acts as a highly sensitive system whereby in the null condition almost complete absorption occurs. Changes in conductivity from the null point will cause a sharp increase in reflected microwave power. This technique will allow electrodeless measurements of both bulk and thick‐film semiconductor properties and may have application as a large‐area detector of infrared radiation.