Semiconductor devices with graphene nanoribbons and methods of manufacture are disclosed. The method includes forming at least one layer of Si material on a substrate. The method further includes forming at least one layer of carbon based material adjacent to the at least one layer of Si. The method further includes patterning at least one of the at least one layer of Si material and the at least one layer of carbon based material. The method further includes forming graphene on the patterned carbon based material.