Half cherry , orn' l
We do not have enough information to answer your question. You did not mention the age of the tree, where it is located in sun or shade, how the tree was cared for, etc.
There may be several reasons for decline such as planting too deeply, drought, too much moisture, possible insect or disease issues such as cherry leaf spot, etc. See our publication on these types of problems and our publication on ornamental fruit trees for more information.
At this point, scratch the branches with your fingernail and look for green tissue. If you see it, the branches are still viable. If you see brown then the branch is dead and you can prune. If there are enough reserves in the root system, the tree should put out new growth next spring.
At that point, you can monitor for symptoms and send us photos of the whole tree, around the base, and affected foliage so we can see what you may be dealing with.
You also have the option of contacting a certified arborist for an on site diagnosis and the best way to proceed.