In semiconductor physics, the Depletion Zone or Depletion layer is a nonconductive region within a conductive, doped semiconductor material where the charge carriers have been swept away. Whereas P and N-doped semiconductors are conductors, the Depletion Zone is an insulator. The existence and shape of Depletion Zones is easily controlled by e-fields, i.e. by voltages applied to the electrodes contacting the semiconductor.

Depletion Zones figure largely in the explanation of the on/off switching of diodes, in the control of the Emitter junction barrier in bipolar junction transistors, in the control of width/length of the conductive channels in field effect transistors, and in the control of the width of the dielectric layer in variable capacitance diodes, "varactors" or "tuning diodes".

A Depletion Zone is essentially an insulator of programmable shape; a nonconducting balloon which invisible grows and shrinks within a block of silicon. Modern electronics is based on transistors, and transistor operation is based on depletion zones.