火花间隙（英语：spark gap，电路中常见符号SG）其组成为两个导体构成的电极，两者之间有一间隙，间隙中可含有气体，比如空气。当两导体之间的电位差高于间隙气体的崩溃电压，此时气体会发生游离，而两导体间会发生电火花，而使其电阻大幅下降。

在游离气体之间的路径尚未中断前会出现电流；此外尚有一最小值的维持电流（holding current），若低于此，电流可能会中断。此情形通常发生在电压下降，然因为气体加热膨胀也可能会导致电流中断。气体游离的过程通常反应剧烈，而产生劈啪声，类似小规模的闪电效果。

历史上，火花间隙常用作电路组件，包括火花间隙发送器、静电式发电机、X光机等。今日最广泛的应用是内燃机的火星塞，但也用在避雷器及其他防止瞬间高压电流的保护设备上。

A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the voltage difference between the conductors exceeds the breakdown voltage of the gas within the gap, a spark forms, ionizing the gas and drastically reducing its electrical resistance. An electric current then flows until the path of ionized gas is broken or the current reduces below a minimum value called the "holding current". This usually happens when the voltage drops, but in some cases occurs when the heated gas rises, stretching out and then breaking the filament of ionized gas. Usually, the action of ionizing the gas is violent and disruptive, often leading to sound (ranging from a snap for a spark plug to thunder for a lightning discharge), light and heat.