A sight for a firearm is provided. The sight is structured to fit within a channel defined within the firearm. In some examples, the channel is defined within the slide of a semi automatic handgun. The sight includes a base that fits within the channel, and a visual index portion extending outward from the base. A removable firearm component blocks an open end of the channel, thereby retaining the sight, when the removable firearm component is installed on the firearm. In some examples, a rear sight may be secured within a channel defined within a slide by a firing pin stop. In other examples, a front sight may be secured within a channel defined within a slide by a barrel bushing. Some examples of the sight may include an adjustment mechanism for moving the visual index portion with respect to the base.