隧道二极管(又称江崎二极管、穿隧效应二极管、穿隧二极管或Tunnel Diode)是一种可以高速切换的半导体，其切换速度可到达微波频率的范围，其原理是利用量子穿隧效应。

隧道二极管是江崎玲于奈1958年8月时发明的，当时他在东京通信工业株式会社（现在的索尼）。1973年时江崎玲于奈和布赖恩·约瑟夫森因为发现上述半导体中的量子穿隧效应而获得诺贝尔物理奖。罗伯特·诺伊斯在为威廉·肖克利工作时也有有关隧道二极管的想法，但没有继续进行研究。

此种二极管是由高掺杂的PN结所形成(空乏区通常只有10奈米宽)，常用的材料包括锗、砷化镓等窄能隙的材料，由于高掺杂会产生晶格的破坏，使得能隙间的缺陷变多，加上窄能隙材料缩小量子穿隧的障碍，所以能够增加量子穿隧的电流。隧道二极管常用于频率转换器和侦测器上，由于隧道二极管的负微分电阻的特性，其也可应用于振荡器、放大器以及开关电路的迟滞。

A tunnel diode or Esaki diode is a type of semiconductor that is capable of very fast operation, well into the microwave frequency region, made possible by the use of the quantum mechanical effect called tunneling.

It was invented in August 1957 by Leo Esaki when he was with Tokyo Tsushin Kogyo, now known as Sony. In 1973 he received the Nobel Prize in Physics, jointly with Brian Josephson, for discovering the electron tunneling effect used in these diodes. Robert Noyce independently came up with the idea of a tunnel diode while working for William Shockley, but was discouraged from pursuing it.