PIN型二极管，又称移相开关二极管，和普通的二层结构的PN结二极管相比，PIN型二极管引入了I层：即在普通PN结二极管的由P型半导体材料组成的P层和由N型半导体材料组成的N层中间，插入一层低掺杂的纯度接近于本征半导体材料组成的I层。如果I层材料为低掺杂的P型半导体，则该二极管可称为π型PIN二极管；如果I层材料为低掺杂的N型半导体，则该二极管可称为ν型PIN二极管。在PIN型二极管中，P层和N层通常由高掺杂的半导体材料组成。由于I层的存在，PIN型二极管通常比普通的二极管拥有更宽的耗尽层，更大的结电阻和更小的结电容。在射频与微波级别的电路中，PIN型二极管经常被用作微波开关、移相器和衰减器。

A PIN diode is a diode with a wide, undoped intrinsic semiconductor region between a p-type semiconductor and an n-type semiconductor region. The p-type and n-type regions are typically heavily doped because they are used for ohmic contacts.

The wide intrinsic region is in contrast to an ordinary PN diode. The wide intrinsic region makes the PIN diode an inferior rectifier (one typical function of a diode), but it makes the PIN diode suitable for attenuators, fast switches, photodetectors, and high voltage power electronics applications.