I need create from these edges semicircle. What can I do this?
Assuming you want to cut a hole in the shape of a semicircle, you can do it easily by erasing the two faces and adding a Subsurface modifier.
Then add two control edgeloops on the sides you want to be flat.
Alternatively, if want a drawn shape instead of a hole, just select one of the radial vertices and use the Spin modifier. The current position of the 3D Cursor will be used as the center. Adjust settings like angle and number of segments as desired.
Enable LoopTools addon in Preferences, choose the lines you want to convert to semi-circle, next look for "LoopTools" found on the Tools tab, then use the 'Circle' widget (found under 'Bridge') and adjust parameters accordingly. Optionally, you could use the "To Sphere" tool (Shift+Alt+S), but it's more 'automatic' and not as configurable.