There is one simple way that you can make a semi-circle in Figma. That is to use the “Intersect selection” tool, which you can find in the toolbar on top of the Figma interface.
To create a semi-circle, first, you have to create a rectangle and a circle. To do this, go to the “Shape tools” at the top-left corner of the toolbar, then select Rectangle. Select Ellipse afterwards.
With this tool selected, just click and drag on the canvas to create the shapes into your desired size.
Next, fill the shapes with color to easily identify them. You can do this by selecting the “Fill” option on the right menu.
Put the two shapes together in such a way that one overlaps the other until the red perpendicular line appears indicating that the edge of the rectangle is exactly at the middle of the circle.
To turn this into a semi circle, simply select the two overlapping shapes, then click on the “boolean groups” tool found at the top-middle part of the page. From there, select the “Intersect selection” option.
Now you can see that we already have a semi-circle. However, this effect is still incomplete because two layers still exist.
To have this effect permanent, select the semi-circle and click on the “boolean groups” tool at the top menu, then select the “Flatten selection” option.
Now you have a one-layer semi-circle!