A semi-automatic pistol is a type of repeating single-chamber handgun (pistol) that automatically cycles its action to insert the subsequent cartridge into the chamber (self-loading), but requires manual actuation of the trigger to actually discharge the following shot. As a result, only one round of ammunition is fired each time the trigger is pulled, as the pistol's fire control group disconnects the trigger mechanism from the firing pin/striker until the trigger has been released and reset.

Additional terms sometimes used as synonyms for a semi-automatic pistol are self-loading pistol, autopistol, autoloading pistol, and automatic pistol (E.G.: Automatic Colt Pistol).

A semi-automatic pistol recycles part of the energy released by the propellant combustion to move its bolt, which is usually housed inside the slide. After a round of ammunition is fired, the spent cartridge casing is extracted and ejected as the slide/bolt moves rearwards under recoil, the hammer/striker is cocked by the slide/bolt movement, and a new round from the magazine is pushed into the chamber when the slide/bolt returns forward under spring tension. This sets up the following shot, which is fired as soon as the trigger is pulled again. Most pistols use a short recoil operation to perform this, but some pistols use simple blowback or gas operation mechanisms.

Most types of semi-automatic pistols rely on a removable box magazine to provide ammunition, which is usually inserted into the grip. However, some pistols are based on receiver-style designs similar to existing semi-automatic rifles, and thus have the magazine inserted separately from the grip.