What is the primary component of a semi-automatic handgun that contains the trigger assembly?

The primary component of a semi-automatic handgun that contains the trigger assembly is the frame. The frame is the structure that houses the internal mechanisms of the firearm, including the trigger system, which is critical for the operation of the handgun. It serves as the foundation to which other components, such as the slide and barrel, are attached. The frame also provides a grip for the shooter and is designed to withstand the forces generated during firing.

In contrast, the slide is responsible for chambering ammunition and ejection of spent cartridges but does not contain the trigger assembly. The barrel is the part of the handgun through which the bullet travels when fired, and it is separate from the mechanism that controls firing. The magazine is where ammunition is stored and fed into the chamber, but it does not play a role in the trigger mechanism itself. Hence, the frame is the correct answer as it encompasses the trigger assembly and its associated parts.