半自动变速器，或自手排变速箱，是可以自动换档的手动变速器，是车用变速器的一种，可在驾驶员的操纵下，通过电子传感器、处理器和执行器来换挡。驾驶员无须像驾驶手动档汽车那样在换档前踩离合器踏板，因为离合器在电子设备的驱动下能自动选择适当的换挡时刻和换挡力矩，快速平稳地转换档位。

单离合器半自动变速器构造简单但最大的缺点在于换档冲击。与之原理类似的是双离合变速器，换档冲击大大降低，但却增加重量变重及可靠度较低的问题。

A semi-automatic transmission (SAT) (also known as a clutchless manual transmission, automated manual transmission, flappy-paddle gear shift, or paddle-shift gearbox) is an automobile transmission that does not change gears automatically, but rather facilitates manual gear changes by dispensing with the need to press a clutch pedal at the same time as changing gears. It uses electronic sensors, pneumatics, processors and actuators to execute gear shifts on input from the driver or by a computer. This removes the need for a clutch pedal which the driver otherwise needs to depress before making a gear change, since the clutch itself is actuated by electronic equipment which can synchronise the timing and torque required to make quick, smooth gear shifts. The system was designed by automobile manufacturers to provide a better driving experience through fast overtaking maneuvers on highways. Some motorcycles also use a system with a conventional gearchange but without the need for manual clutch operation.