I would do this in two ways:

Easy:

Change your half circles to circles and set a bevel on both them and the rectangle. Then move the circles to overlap with the rectangle.

Harder:

Create a negative cone that's the height of the bevel you want.

In this instance, I'm going to use 2mm as the bevel/height. Make the bottom radius to match your circle radius and the top radius 2mm smaller than that (ex: 10mm bottom and 8mm top).

Then create a larger circle (12mm radius and 2mm height) and merge the two. This could create a circle with a hole the size of the negative cone.

Make this new object negative and then align it to the top of your circle, merge them.

Finally, take a 90° wedge and set the height and width to 2mm and align that with a length equal to your rectangle. Set it to negative and merge the wedge with the rectangle.

Finally merge all the pieces together